CA1114954A - Digital sound synthesizer - Google Patents
Digital sound synthesizerInfo
- Publication number
- CA1114954A CA1114954A CA330,178A CA330178A CA1114954A CA 1114954 A CA1114954 A CA 1114954A CA 330178 A CA330178 A CA 330178A CA 1114954 A CA1114954 A CA 1114954A
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- signal
- tone
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- signals
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10H—ELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE
- G10H7/00—Instruments in which the tones are synthesised from a data store, e.g. computer organs
- G10H7/02—Instruments in which the tones are synthesised from a data store, e.g. computer organs in which amplitudes at successive sample points of a tone waveform are stored in one or more memories
- G10H7/06—Instruments in which the tones are synthesised from a data store, e.g. computer organs in which amplitudes at successive sample points of a tone waveform are stored in one or more memories in which amplitudes are read at a fixed rate, the read-out address varying stepwise by a given value, e.g. according to pitch
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- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Electrophonic Musical Instruments (AREA)
- Noise Elimination (AREA)
Abstract
DIGITAL SOUND SYNTHESIZER
Abstract of the Disclosure A digital sound synthesizer produces a variable spectral line width to synthesize tones by accumulating phase quanta sequentially for each of a set of tone samples. The rate of accumulation of phase for each tone is randomly altered with preset values of phase increment to broaden the spectral line.
The broadened-spectral lines provide a display with a spectral presentation of sounds more closely resembling naturally occurring sounds.
Abstract of the Disclosure A digital sound synthesizer produces a variable spectral line width to synthesize tones by accumulating phase quanta sequentially for each of a set of tone samples. The rate of accumulation of phase for each tone is randomly altered with preset values of phase increment to broaden the spectral line.
The broadened-spectral lines provide a display with a spectral presentation of sounds more closely resembling naturally occurring sounds.
Description
Background of the Invention The digital synthesis of a tone of a specified frequency is described in a paper entitled "A Digital Frequency Synthesizer"
by J. Tierney, C. M. Rader and B. Gold which appeared in the IEEE Transactions on Audio Electroacoustics, vol. AU-l9, at pages 48-56, in March 1971. The technique described therein utilizes digital techniques followed by analog filtering to produce an analog tone of a prescribed frequency.
It has been found useful to synthesize sounds composed of a plurality of tones for training people to recognize specific sounds. Such sounds may be recognized auditorily as by playing the sounds through a loud speaker, or visually as by passing the sound through a spectrum analyzer and displaying the spectrum to produce a visually identifiable signature of the sound spectrum. For example, such a sound synthesizer may be utilized in the training of automotive mechanics to recognize specific sounds in an automobile engine, which sounds may be masked by other sounds or noise of the engine. Recognition of the specific sounds would be useful in identifying the presence of a specific malfunction in the engine.
` A problem has arisen in the past when a sound synthesizer has been utilized with a visible display of the spectral signature due to the fact that a spectral analysis of a naturally occurring sound, such as the sound of an automobile engine, produces relatively broad spectral lines at various ones of the tone frequencies present in the sound. In contrast, the sounds produced by synthesizers of the prior art and composed of a plurality of tone frequencies result in a spectral signature showing relatively sharp spectral lines at the respective tone frequencies. The difference in line width makes recognition of the spectral signature more difficult and decreases the utility of the sound synthesis technique as a means for teaching the identification of specific sound patterns.
Summary of the Invention The aforementioned problem is overcome and other ad-vantages are provided by a synthesizer which digitally produces sounds composed of a set of tones and provides a selectably variable spectral line width to the synthesized tones. The phase of each tone is obtained by accumulating phase quanta, the value of accumulated phase increasing at a rate pToportional to the frequency of each tone. In accordance with the invention, the rate of accumulation of phase for each tone is randomly altered by a preset value of phase increment which is added algebraically to the phase quanta with positive and negative signs of the increment occurring substantially randomly in response to a pseudo-random noise source. The synthesizer produces a plurality of tones simultaneously by providing separate accumulations of quanta of phase for each tone during each sample interval, using the separate accumu-lations of phase to address a memory for converting the accumu-lations of phase to samples of sinusoids of the specific tones, and then summing together the respective sinusoids of the tones to p~rovide a sum of tone-like electrical signals which are connected by a speaker to the audible tones. There is also disclosed a multiplier for scaling the amplitudes of the individual tones prior to their summation to produce the output sound signal, as well as a timing circuit including the addressing of a memory for altering the aforesaid magnitudes in accordance with a predetermined temporal pattern for the synthesis of a sound more accurately representing a - naturally occuring sound.
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In accordance with the present invention, there is provided a sound synthesizer comprising:
means for accumulating predetermined quanta of phase during the generation of a tone of said sound to produce a phase angle;
means coupled to said accumulating means for converting said phase angle into a signal having a sinusoidal waveform at a frequency proportional to the rate of increase of said phase angle;
means for generating randomly occurring quanta of phase; and means coupled to an input terminal of said accumulating means for summing said randomly occurring quanta of phase with said predetermined quanta of phase prior to said accumulating to broaden the spectral line of said tone~
In accordance with another aspect of the invention, ~r there is provided a synthesizer of a tone-like signal comprising:
. means for storing first and second signals;
Y an integrator;
means for directly coupling said first signalfrom said storing means to said integrator;
means for randomly coupling said second signal from said storing means to said integrator; and means coupled to an output terminal of said integrator for converting integrated values of said first and said second signals into a tone-like signal having a spectrum in the form of a broadened line spectrum.
In accordance with another aspect of the invention, there is provided a synthesizer of a set of tone-like signals of broadened bandwidth comprising:
first and second storage means storing respectively first and second signals each of which represents a magnitude of - 3a -frequency;
means for combining said first and said second signals to provide a combined signal;
timing means coupled to said first and said second storage means for repetitively coupling said first signal and said second signal at a predetermined rate to said combining means;
noise generator means coupled to said timing means and said combining means for activating said combining means to 10 produce a substantially random sequence of sums and differences of said first and said second signals;
means for integrating said combined signal to produce an integrated signal representing a phase;
means for converting said integrated signal to a tone-like signal; and means for scaling said tone-like signal.
In accordance with another aspect of the invention, there is provided in combination:
means for storing first and second signals;
means responsive to an input signal for generatlng a tone-like signal having a~frequency proportlonal to said input signal;
means for directly coupling said first signal from said storing means to said generating means to provide a frequency of said tone-like signal proportional to said flrst signal; and wherein said coupling means includes means for randomly combin-- ing said second signal with said first signal to provide said input signal, said second signal introducing a broadened spectrum 30 to said tone-like signal.
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Brief Description of the Drawing The aforementioned aspects and other features of the invention are explained in the following description taken in connection with the accompanying drawing which shows a block diagram of the sound synthesizer of the invention, the figure showing a pseudo-random noise.generator for randomly incrementing the phases of the tones of the sound.
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. , ., . 30 .~ -4-Description of the Preferred Embodiment Referring now to the figure, a sound synthesizer 20 comprises, in accordance with the invention, six memories 21-26, counters 29-30, a clock 33, adders 37-39, a frequency divider 40, a pseudo-random noise generator 42, a multiplier 44, an address generator 46, an accumulator 48, a register 50, a digital-to-analog converter 51, a low pass filter 54, a spectrum analyzer 56, a speaker 50 and a display 62. The adder 38 in cooperation with the memory 25 perform the function of an integrator, identified by the legend 64, which converts frequency on line 66 to phase on line 68 for each of the tones produced by the synthesizer 20.
In describing the operation of the synthesizer 20 for the production of a set of tones, an exemplary set of one-hundred tones is assumed with the lowest tone having the frequency of 40 Hz ~hertz) and the highest tone having a frequency of 4,000 Hz. Considering first the production of a single tone, namely, the highest tone at 4,000 Hz, digital samples of the tone appear in the register 50 at a rate above the Nyquist sampling rate. The tone samples appearing in the register 50 are then converted by the converter 51 to analog signal samples and filtered by the low pass filter 54 to produce an electrical signal having a sinusoidal waveform at the 4,000 Hz frequency of the highest tone. By way of example, it is assumed that four samples of a tone appear in the register 50 for each cycle of the sinusoidal signal produced by the filter 54. The resulting sampling rate is 16,000 Hz. The magnitude of the sampling rate - has been selected on the basis of the frequency of the highest tone, the same sampling rate is to be utilized for synthesizing each of the other ninety-nine tones. The sinusoidal electrical . - . . ~ , , signal representing the 4,000 Hz tone, produced by the filter 54, as well as the corresponding signals representing the other tones, are applied to the speaker 60 to produce an audible sound.
The counter 29 counts modulo N where N is equal to the number of tones, N being equal to 100 for the present exemplary set of one-hundred tones. Each sound produced by the speaker 60 is formed from the set of one-hundTed tones wherein the tones are scaled in amplitude by the multiplier 44 to provide a set of amplitude values, including 0, for respective ones of the tones. A scaling factor of 0 is utilized when it is desired that a specific tone is to be absent in the sound produced by the speaker 60. The counter 29 produces an address signal on line 70 for designating sequentially each of the tones in the set of tones, irrespectively of the amplitudes to be impressed upon the tones by the multiplier 44. Thus, the counter 29 cycles repetitively through each of the tone addresses and provides a pulse signal on line 72 upon the completion of each cycle of addressing the tones.
The clock 33 applies clock pulses to the counter 29 at a rate sufficient to provide the aforementioned sampling rate of 16,000 Hz for each of the one-hundred tones. Accordingly, the clock 33 provides pulses at a rate of 1.6 MHz ~megahertz). Since the counter counts modulo N, where N = lO0, the counter 29 cycles through the one-hundred addresses at the aforementioned rate of -~ 16,000 Hz. The tone address on line 70 is applied to each of the memories 21-25.
With reference to the 4,000 Hz tone, since four samples of the tone are produced during each cycle of the tone, it follows - 30 that each sample represents an increment in phase of 9~ of the sinusoidal signal appearing at the output of the filter 54.
Since the 16,000 Hz sampling rate applies to each of the tones, a tone of 400 Hz, which has a period which is ten times longer than the period of the 4,000 Hz tone, receives 40 samples per period of the tone wherein each sample represents a phase increment of 9. For the lowest tone of 40 Hz, wherein the period is one-hundred times longer than the period of the 4,000 Hz tone, there are 400 samples per period of the tone wherein each sample represents a phase increment of 0.9. The memory 21 provides the requisite phase increments at the 16,000 Hz sample rate for each of the tones in accordance with the - addressing of the memory 21 by the address on line 70 from the counter 29. Each of the phase increments is coupled from the memory 21 via the adder 37 to the integrator 64. To facilitate the explanation, it is assumed at this point that the memory 22 and the noise generator 42 are inactive so that the output signal of the adder 37 on line 66 equals the phase increment - provided by the memory 21. Thus, for each of the tones being produced, the corresponding phase increment, as represented by the digital signal on line 66, is proportional to the frequency of the tone. As noted hereinabove, in the case of the 40 Hz tone, each phase increment appearing on line 66 has a value of 0.9 while the corresponding phase increment for the 4,000 Hz tone has a value of 90. The phase increments for both the 40 Hz tone and the 4,000 Hz tone appear at the same sampling rate, namely, the aforementioned 16,000 Hz rate. In view of the fact that the signals on line 66 are proportional to the tone frequency, the input signal to the integrator 64 on line 66 has been designated in the figure as the tone frequency.
The integrator 64 operates as a digital accumulator for summing together, modulo 360, successively occurring phase increments on line 66 for each of the respective tones.
Considering the exemplary tone of 4,000 Hz, a 90 phase increment is added by the adder 38 to a value of phase previ-ously stored in the memory 25. Assuming an exemplary value of zero phase initially stored in the memory 25, the digital signals appearing on line 68 at the output of the integrator 64 have the following set of values for successive samples of the 4,000 Hz tone, namely, 0, 90, 180, 270, 0, 90, wherein the sequence is seen to repeat due to the modulo 360 addition provided by the adder 38. Since the value of the digital signal on line 68 is seen to increase linearly with time in a modulo 360 fashion, it is apparent that the signal on line 68 represents the phase of the corresponding sinusoidal signal : at thé output of the filter 54.
Since the memory 25 is to be utilized for storing values of phase for each of the one-hundred tones, the memory 25 is pro-vided with one-hundred sections which are sequentially addressed by the address on line 70 in accordance with the particular tone for which a sample is appearing on line 66. Accordingly, the output signal of the adder 38 is coupled into and stored in the specific section of the memory 25 as addressed by the address on line 70. The signal stored in that section of the memory 25 is retained until the counter 29 has completed a full cycle of its counting whereupon the address of the corresponding tone again appears on line 70 so that the previous output signal of the adder 38 as stored in the memory 25 is applied to an input terminal of the adder 38.
: The phase angle appearing on line 68 is coupled via the adder 39 to the memory 26 and is converted by the memory 26 to -the corresponding value of the sinusoidal signal produced by the filter 54. To facilitate the explanation, it is assumed at this point that the memory 23 is inactive so that the output terminal of the adder 39 shows the same value of phase as is present on line 68. The memory 26 provides a set of values of sine which are addressed by the corresponding phase angles at the output terminal of the adder 39. Thus, for each value of phase angle on line 68, the memory 26 applies the corresponding magnitude of a normalized sinusoid to an input terminal of the multiplier 44 which then scales the normalized value of the sinusoid to produce the desired amplitude for the sinusoidal signal of the filter 54.
- In the case where several non-zero values of tones are to be produced, the scaled amplitudes of the samples for each tone are applied by the multiplier 44 to the accumulator 48 which sums together the samples of all the tones produced during one cycling of the counter 29. The memory 24 provides amplitude scale factors for the multiplier 44 for use in scaling the amplitudes of the samples of the respective tones. Thereby, the output signal of the accumulator 48 represents a sample of the sum of the tones in the sound produced by the speaker 60. The sum of the samples of the accumulator 48 is coupled to the register 50 where they are stored to permit the conversion to analog samples by the converter 51. The signal on line 72 serves to strobe the register 50 for receiving the sum of the samples, and to clear : the accumulator 48 upon the transfer of the sum of the samples to the register 50. A delay unit 74 delays application of the signal on line 72 for clearing the accumulator 48 until after the strobing of the register 50.
A visual presentation of the spectral signature of the g , sounds at the speaker 60 is provided by the spectrum analyzer 56 and the display 62. The analyzer 56 provides the spectral data within bands having a width of, for example, one Hz so that the spectral signatures of similar sounds can be distinguished.
The memory 23 provides an initial phase angle to the sinusoidal signals of each of the tones appearing at the output terminal of the filter 54. These phase angles may be inserted - directly into the memory 25 prior to the generation of the sound by the synthesizer 20 in the event that these phase angles are to remain unchanged during the entire period of the generation of the sound or, as shown in the figure, may be added to the output signal of the integrator 64 by the adder 39. The use of the adder 39 permits a changing of the phase angle during the generation of the sound and thereby provides the facility for altering a characteristic of the sound. The phase angle of the memory 23 appears as a fixed phase offset in the sequence of phases appearing on line 68 for each tone.
Addressing of the memories 21, 22, 23 and 24 is accomplished by a composite address including the tone address on line 70 and a program address on line 76. The program address on line 76 is provided by the address generator 46 in response to a count provided by the counter 30. The counter 30 is rese~ by a reset button 78 at the beginning of the generation of sound by the synthesizer 20, and thereafter counts the pulse signals on line 72. After each of a predetermined number of counts by the counter 30, the address generator 46 in response to the counts of a predetermined set of the counts updates the address on line 76.
The memories 21-24 are provided with separate compartments corre-sponding to each address of the program on line 76. Within each ~ c~
compartment, the tone address on line 70 designates the specific tone for which phase is being accumulated and for which amplitude scale factors are to be applied. Thus, it is seen that the address generator 46 permits a variation of the relative phase offsets between the tones as provided by the memory 23, a variation in the pattern of the relative amplitudes of the tones as provided by the memory 24, a variation in fre-quency as provided by the memory 21, and a variation in spectral line width (to be described below) by the memory 22. Thereby, for example, after a few seconds of sound have elapsed, certain tones may be dropped from the sound by providing a zero value of scaling while other tones may be inserted into the sound. In this way, the address generator 46 provides for a varying of the initial phases of .the tones as well as for the variation in their respective amplitudes and frequencies during the duration of the sound to provide greater flexibility in the synthesis of a sound similar to that occurring in nature. The memories 21, 22, 23 and 24 are each provided with keyboards for the entry of - the specific values of frequency, spectral line width, initial ` 20 phase, and amplitude respectively.
The feature of the invention relating to the broadening of spectral lines appearing on the display 62 is accomplished by the memory 22, the frequency divider 40 and the noise generator 42.
The divider 40 divides the aforementioned 1.6 MHz pulse repetition frequency of the clock 33 to produce clock pulses at a pulse - repetition frequency of, for example, approximately 40 Hz. The clock pulses from the divider 40 drive the generator 42. The - generator 42 produces a pseudo-random noise code in the form of logic signals having states which vary between 0 and 1. The construction of such generators is well known, one such generator '11-being described in Figure 2 in the United States Patent 3,818,478 which issued in the name of H. L. Groginsky on June 18, 1974. The signal produced by the generator 42 serves as a sign bit for the digital signals provided by the memory 22 in response to the addressing thereof by the address on line 70. Since the digital numbers provided for each of the tones by the memory 22 are summed algebraically ~either addition or subtraction according to the sign bit) to the digital numbers of the memory 21 by the adder 37, the digital numbers stored in the memory 22 for each of the tones is referred to as a frequency increment. Thus, the frequency increment is applied in a random fashion, with addition and subtraction of the frequency increment averaging out to zero over the total length of the maximal length -~ shift register code of the generator 42. A keyboard on the memory 22 permits entry of individual amounts of frequency increment - for each of the tones. The clock pulse frequency applied to the generator 42 is greater than the frequency increment provided by the successive application of phase quanta as designated by the memory 22 to provide a phase modulation index to the noise process which is less than unity. Thereby, a spectral line displayed by the analyzer 56 on the display 62 is uniformly broadened without the appearance of discrete sideband spectral lines. Accordingly, the display 62 shows broadened spectral line patterns which corre-spond more closely with the spectral signatures obtained from naturally produced sound.
It is understood that the above-described embodiment of the invention is illustrative only and that modifications thereof may ; occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiment disclosed ; 30 herein but it to be limited only as defined by the appended claims.,
by J. Tierney, C. M. Rader and B. Gold which appeared in the IEEE Transactions on Audio Electroacoustics, vol. AU-l9, at pages 48-56, in March 1971. The technique described therein utilizes digital techniques followed by analog filtering to produce an analog tone of a prescribed frequency.
It has been found useful to synthesize sounds composed of a plurality of tones for training people to recognize specific sounds. Such sounds may be recognized auditorily as by playing the sounds through a loud speaker, or visually as by passing the sound through a spectrum analyzer and displaying the spectrum to produce a visually identifiable signature of the sound spectrum. For example, such a sound synthesizer may be utilized in the training of automotive mechanics to recognize specific sounds in an automobile engine, which sounds may be masked by other sounds or noise of the engine. Recognition of the specific sounds would be useful in identifying the presence of a specific malfunction in the engine.
` A problem has arisen in the past when a sound synthesizer has been utilized with a visible display of the spectral signature due to the fact that a spectral analysis of a naturally occurring sound, such as the sound of an automobile engine, produces relatively broad spectral lines at various ones of the tone frequencies present in the sound. In contrast, the sounds produced by synthesizers of the prior art and composed of a plurality of tone frequencies result in a spectral signature showing relatively sharp spectral lines at the respective tone frequencies. The difference in line width makes recognition of the spectral signature more difficult and decreases the utility of the sound synthesis technique as a means for teaching the identification of specific sound patterns.
Summary of the Invention The aforementioned problem is overcome and other ad-vantages are provided by a synthesizer which digitally produces sounds composed of a set of tones and provides a selectably variable spectral line width to the synthesized tones. The phase of each tone is obtained by accumulating phase quanta, the value of accumulated phase increasing at a rate pToportional to the frequency of each tone. In accordance with the invention, the rate of accumulation of phase for each tone is randomly altered by a preset value of phase increment which is added algebraically to the phase quanta with positive and negative signs of the increment occurring substantially randomly in response to a pseudo-random noise source. The synthesizer produces a plurality of tones simultaneously by providing separate accumulations of quanta of phase for each tone during each sample interval, using the separate accumu-lations of phase to address a memory for converting the accumu-lations of phase to samples of sinusoids of the specific tones, and then summing together the respective sinusoids of the tones to p~rovide a sum of tone-like electrical signals which are connected by a speaker to the audible tones. There is also disclosed a multiplier for scaling the amplitudes of the individual tones prior to their summation to produce the output sound signal, as well as a timing circuit including the addressing of a memory for altering the aforesaid magnitudes in accordance with a predetermined temporal pattern for the synthesis of a sound more accurately representing a - naturally occuring sound.
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In accordance with the present invention, there is provided a sound synthesizer comprising:
means for accumulating predetermined quanta of phase during the generation of a tone of said sound to produce a phase angle;
means coupled to said accumulating means for converting said phase angle into a signal having a sinusoidal waveform at a frequency proportional to the rate of increase of said phase angle;
means for generating randomly occurring quanta of phase; and means coupled to an input terminal of said accumulating means for summing said randomly occurring quanta of phase with said predetermined quanta of phase prior to said accumulating to broaden the spectral line of said tone~
In accordance with another aspect of the invention, ~r there is provided a synthesizer of a tone-like signal comprising:
. means for storing first and second signals;
Y an integrator;
means for directly coupling said first signalfrom said storing means to said integrator;
means for randomly coupling said second signal from said storing means to said integrator; and means coupled to an output terminal of said integrator for converting integrated values of said first and said second signals into a tone-like signal having a spectrum in the form of a broadened line spectrum.
In accordance with another aspect of the invention, there is provided a synthesizer of a set of tone-like signals of broadened bandwidth comprising:
first and second storage means storing respectively first and second signals each of which represents a magnitude of - 3a -frequency;
means for combining said first and said second signals to provide a combined signal;
timing means coupled to said first and said second storage means for repetitively coupling said first signal and said second signal at a predetermined rate to said combining means;
noise generator means coupled to said timing means and said combining means for activating said combining means to 10 produce a substantially random sequence of sums and differences of said first and said second signals;
means for integrating said combined signal to produce an integrated signal representing a phase;
means for converting said integrated signal to a tone-like signal; and means for scaling said tone-like signal.
In accordance with another aspect of the invention, there is provided in combination:
means for storing first and second signals;
means responsive to an input signal for generatlng a tone-like signal having a~frequency proportlonal to said input signal;
means for directly coupling said first signal from said storing means to said generating means to provide a frequency of said tone-like signal proportional to said flrst signal; and wherein said coupling means includes means for randomly combin-- ing said second signal with said first signal to provide said input signal, said second signal introducing a broadened spectrum 30 to said tone-like signal.
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Brief Description of the Drawing The aforementioned aspects and other features of the invention are explained in the following description taken in connection with the accompanying drawing which shows a block diagram of the sound synthesizer of the invention, the figure showing a pseudo-random noise.generator for randomly incrementing the phases of the tones of the sound.
:
. , ., . 30 .~ -4-Description of the Preferred Embodiment Referring now to the figure, a sound synthesizer 20 comprises, in accordance with the invention, six memories 21-26, counters 29-30, a clock 33, adders 37-39, a frequency divider 40, a pseudo-random noise generator 42, a multiplier 44, an address generator 46, an accumulator 48, a register 50, a digital-to-analog converter 51, a low pass filter 54, a spectrum analyzer 56, a speaker 50 and a display 62. The adder 38 in cooperation with the memory 25 perform the function of an integrator, identified by the legend 64, which converts frequency on line 66 to phase on line 68 for each of the tones produced by the synthesizer 20.
In describing the operation of the synthesizer 20 for the production of a set of tones, an exemplary set of one-hundred tones is assumed with the lowest tone having the frequency of 40 Hz ~hertz) and the highest tone having a frequency of 4,000 Hz. Considering first the production of a single tone, namely, the highest tone at 4,000 Hz, digital samples of the tone appear in the register 50 at a rate above the Nyquist sampling rate. The tone samples appearing in the register 50 are then converted by the converter 51 to analog signal samples and filtered by the low pass filter 54 to produce an electrical signal having a sinusoidal waveform at the 4,000 Hz frequency of the highest tone. By way of example, it is assumed that four samples of a tone appear in the register 50 for each cycle of the sinusoidal signal produced by the filter 54. The resulting sampling rate is 16,000 Hz. The magnitude of the sampling rate - has been selected on the basis of the frequency of the highest tone, the same sampling rate is to be utilized for synthesizing each of the other ninety-nine tones. The sinusoidal electrical . - . . ~ , , signal representing the 4,000 Hz tone, produced by the filter 54, as well as the corresponding signals representing the other tones, are applied to the speaker 60 to produce an audible sound.
The counter 29 counts modulo N where N is equal to the number of tones, N being equal to 100 for the present exemplary set of one-hundred tones. Each sound produced by the speaker 60 is formed from the set of one-hundTed tones wherein the tones are scaled in amplitude by the multiplier 44 to provide a set of amplitude values, including 0, for respective ones of the tones. A scaling factor of 0 is utilized when it is desired that a specific tone is to be absent in the sound produced by the speaker 60. The counter 29 produces an address signal on line 70 for designating sequentially each of the tones in the set of tones, irrespectively of the amplitudes to be impressed upon the tones by the multiplier 44. Thus, the counter 29 cycles repetitively through each of the tone addresses and provides a pulse signal on line 72 upon the completion of each cycle of addressing the tones.
The clock 33 applies clock pulses to the counter 29 at a rate sufficient to provide the aforementioned sampling rate of 16,000 Hz for each of the one-hundred tones. Accordingly, the clock 33 provides pulses at a rate of 1.6 MHz ~megahertz). Since the counter counts modulo N, where N = lO0, the counter 29 cycles through the one-hundred addresses at the aforementioned rate of -~ 16,000 Hz. The tone address on line 70 is applied to each of the memories 21-25.
With reference to the 4,000 Hz tone, since four samples of the tone are produced during each cycle of the tone, it follows - 30 that each sample represents an increment in phase of 9~ of the sinusoidal signal appearing at the output of the filter 54.
Since the 16,000 Hz sampling rate applies to each of the tones, a tone of 400 Hz, which has a period which is ten times longer than the period of the 4,000 Hz tone, receives 40 samples per period of the tone wherein each sample represents a phase increment of 9. For the lowest tone of 40 Hz, wherein the period is one-hundred times longer than the period of the 4,000 Hz tone, there are 400 samples per period of the tone wherein each sample represents a phase increment of 0.9. The memory 21 provides the requisite phase increments at the 16,000 Hz sample rate for each of the tones in accordance with the - addressing of the memory 21 by the address on line 70 from the counter 29. Each of the phase increments is coupled from the memory 21 via the adder 37 to the integrator 64. To facilitate the explanation, it is assumed at this point that the memory 22 and the noise generator 42 are inactive so that the output signal of the adder 37 on line 66 equals the phase increment - provided by the memory 21. Thus, for each of the tones being produced, the corresponding phase increment, as represented by the digital signal on line 66, is proportional to the frequency of the tone. As noted hereinabove, in the case of the 40 Hz tone, each phase increment appearing on line 66 has a value of 0.9 while the corresponding phase increment for the 4,000 Hz tone has a value of 90. The phase increments for both the 40 Hz tone and the 4,000 Hz tone appear at the same sampling rate, namely, the aforementioned 16,000 Hz rate. In view of the fact that the signals on line 66 are proportional to the tone frequency, the input signal to the integrator 64 on line 66 has been designated in the figure as the tone frequency.
The integrator 64 operates as a digital accumulator for summing together, modulo 360, successively occurring phase increments on line 66 for each of the respective tones.
Considering the exemplary tone of 4,000 Hz, a 90 phase increment is added by the adder 38 to a value of phase previ-ously stored in the memory 25. Assuming an exemplary value of zero phase initially stored in the memory 25, the digital signals appearing on line 68 at the output of the integrator 64 have the following set of values for successive samples of the 4,000 Hz tone, namely, 0, 90, 180, 270, 0, 90, wherein the sequence is seen to repeat due to the modulo 360 addition provided by the adder 38. Since the value of the digital signal on line 68 is seen to increase linearly with time in a modulo 360 fashion, it is apparent that the signal on line 68 represents the phase of the corresponding sinusoidal signal : at thé output of the filter 54.
Since the memory 25 is to be utilized for storing values of phase for each of the one-hundred tones, the memory 25 is pro-vided with one-hundred sections which are sequentially addressed by the address on line 70 in accordance with the particular tone for which a sample is appearing on line 66. Accordingly, the output signal of the adder 38 is coupled into and stored in the specific section of the memory 25 as addressed by the address on line 70. The signal stored in that section of the memory 25 is retained until the counter 29 has completed a full cycle of its counting whereupon the address of the corresponding tone again appears on line 70 so that the previous output signal of the adder 38 as stored in the memory 25 is applied to an input terminal of the adder 38.
: The phase angle appearing on line 68 is coupled via the adder 39 to the memory 26 and is converted by the memory 26 to -the corresponding value of the sinusoidal signal produced by the filter 54. To facilitate the explanation, it is assumed at this point that the memory 23 is inactive so that the output terminal of the adder 39 shows the same value of phase as is present on line 68. The memory 26 provides a set of values of sine which are addressed by the corresponding phase angles at the output terminal of the adder 39. Thus, for each value of phase angle on line 68, the memory 26 applies the corresponding magnitude of a normalized sinusoid to an input terminal of the multiplier 44 which then scales the normalized value of the sinusoid to produce the desired amplitude for the sinusoidal signal of the filter 54.
- In the case where several non-zero values of tones are to be produced, the scaled amplitudes of the samples for each tone are applied by the multiplier 44 to the accumulator 48 which sums together the samples of all the tones produced during one cycling of the counter 29. The memory 24 provides amplitude scale factors for the multiplier 44 for use in scaling the amplitudes of the samples of the respective tones. Thereby, the output signal of the accumulator 48 represents a sample of the sum of the tones in the sound produced by the speaker 60. The sum of the samples of the accumulator 48 is coupled to the register 50 where they are stored to permit the conversion to analog samples by the converter 51. The signal on line 72 serves to strobe the register 50 for receiving the sum of the samples, and to clear : the accumulator 48 upon the transfer of the sum of the samples to the register 50. A delay unit 74 delays application of the signal on line 72 for clearing the accumulator 48 until after the strobing of the register 50.
A visual presentation of the spectral signature of the g , sounds at the speaker 60 is provided by the spectrum analyzer 56 and the display 62. The analyzer 56 provides the spectral data within bands having a width of, for example, one Hz so that the spectral signatures of similar sounds can be distinguished.
The memory 23 provides an initial phase angle to the sinusoidal signals of each of the tones appearing at the output terminal of the filter 54. These phase angles may be inserted - directly into the memory 25 prior to the generation of the sound by the synthesizer 20 in the event that these phase angles are to remain unchanged during the entire period of the generation of the sound or, as shown in the figure, may be added to the output signal of the integrator 64 by the adder 39. The use of the adder 39 permits a changing of the phase angle during the generation of the sound and thereby provides the facility for altering a characteristic of the sound. The phase angle of the memory 23 appears as a fixed phase offset in the sequence of phases appearing on line 68 for each tone.
Addressing of the memories 21, 22, 23 and 24 is accomplished by a composite address including the tone address on line 70 and a program address on line 76. The program address on line 76 is provided by the address generator 46 in response to a count provided by the counter 30. The counter 30 is rese~ by a reset button 78 at the beginning of the generation of sound by the synthesizer 20, and thereafter counts the pulse signals on line 72. After each of a predetermined number of counts by the counter 30, the address generator 46 in response to the counts of a predetermined set of the counts updates the address on line 76.
The memories 21-24 are provided with separate compartments corre-sponding to each address of the program on line 76. Within each ~ c~
compartment, the tone address on line 70 designates the specific tone for which phase is being accumulated and for which amplitude scale factors are to be applied. Thus, it is seen that the address generator 46 permits a variation of the relative phase offsets between the tones as provided by the memory 23, a variation in the pattern of the relative amplitudes of the tones as provided by the memory 24, a variation in fre-quency as provided by the memory 21, and a variation in spectral line width (to be described below) by the memory 22. Thereby, for example, after a few seconds of sound have elapsed, certain tones may be dropped from the sound by providing a zero value of scaling while other tones may be inserted into the sound. In this way, the address generator 46 provides for a varying of the initial phases of .the tones as well as for the variation in their respective amplitudes and frequencies during the duration of the sound to provide greater flexibility in the synthesis of a sound similar to that occurring in nature. The memories 21, 22, 23 and 24 are each provided with keyboards for the entry of - the specific values of frequency, spectral line width, initial ` 20 phase, and amplitude respectively.
The feature of the invention relating to the broadening of spectral lines appearing on the display 62 is accomplished by the memory 22, the frequency divider 40 and the noise generator 42.
The divider 40 divides the aforementioned 1.6 MHz pulse repetition frequency of the clock 33 to produce clock pulses at a pulse - repetition frequency of, for example, approximately 40 Hz. The clock pulses from the divider 40 drive the generator 42. The - generator 42 produces a pseudo-random noise code in the form of logic signals having states which vary between 0 and 1. The construction of such generators is well known, one such generator '11-being described in Figure 2 in the United States Patent 3,818,478 which issued in the name of H. L. Groginsky on June 18, 1974. The signal produced by the generator 42 serves as a sign bit for the digital signals provided by the memory 22 in response to the addressing thereof by the address on line 70. Since the digital numbers provided for each of the tones by the memory 22 are summed algebraically ~either addition or subtraction according to the sign bit) to the digital numbers of the memory 21 by the adder 37, the digital numbers stored in the memory 22 for each of the tones is referred to as a frequency increment. Thus, the frequency increment is applied in a random fashion, with addition and subtraction of the frequency increment averaging out to zero over the total length of the maximal length -~ shift register code of the generator 42. A keyboard on the memory 22 permits entry of individual amounts of frequency increment - for each of the tones. The clock pulse frequency applied to the generator 42 is greater than the frequency increment provided by the successive application of phase quanta as designated by the memory 22 to provide a phase modulation index to the noise process which is less than unity. Thereby, a spectral line displayed by the analyzer 56 on the display 62 is uniformly broadened without the appearance of discrete sideband spectral lines. Accordingly, the display 62 shows broadened spectral line patterns which corre-spond more closely with the spectral signatures obtained from naturally produced sound.
It is understood that the above-described embodiment of the invention is illustrative only and that modifications thereof may ; occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiment disclosed ; 30 herein but it to be limited only as defined by the appended claims.,
Claims (13)
1. A sound synthesizer comprising:
means for accumulating predetermined quanta of phase during the generation of a tone of said sound to produce a phase angle;
means coupled to said accumulating means for converting said phase angle into a signal having a sinusoidal waveform at a frequency proportional to the rate of increase of said phase angle;
means for generating randomly occurring quanta of phase;
and means coupled to an input terminal of said accumulating means for summing said randomly occurring quanta of phase with said predetermined quanta of phase prior to said accumulating to broaden the spectral line of said tone.
means for accumulating predetermined quanta of phase during the generation of a tone of said sound to produce a phase angle;
means coupled to said accumulating means for converting said phase angle into a signal having a sinusoidal waveform at a frequency proportional to the rate of increase of said phase angle;
means for generating randomly occurring quanta of phase;
and means coupled to an input terminal of said accumulating means for summing said randomly occurring quanta of phase with said predetermined quanta of phase prior to said accumulating to broaden the spectral line of said tone.
2. A synthesizer according to Claim 1 further comprising a memory for storing said predetermined phase quanta, said memory further storing predetermined phase quanta of differing amounts to produce tones of differing frequencies; and means for addressing said memory for sequentially introducing the phase quanta corresponding to each of a set of tones of said sound into said accumulator for simultaneously generating said tones.
3. A synthesizer according to Claim 2 further comprising means coupled to said addressing means for scaling the amplitudes of individual ones of said tones, said scaling means including a memory for storing scaling factors, said memory being ad-dressed by said addressing means for applying said scaling factors in the scaling of individual ones of said tones corresponding to addresses of said addressing means.
4. A synthesizer of a tone-like signal comprising:
means for storing first and second signals;
an integrator;
means for directly coupling said first signal from said storing means to said integrator;
means for randomly coupling said second signal from said storing means to said integrator; and means coupled to an output terminal of said integrator for converting integrated values of said first and said second signals into a tone-like signal having a spectrum in the form of a broadened line spectrum.
means for storing first and second signals;
an integrator;
means for directly coupling said first signal from said storing means to said integrator;
means for randomly coupling said second signal from said storing means to said integrator; and means coupled to an output terminal of said integrator for converting integrated values of said first and said second signals into a tone-like signal having a spectrum in the form of a broadened line spectrum.
5. A synthesizer according to Claim 4 wherein said randomly coupling means comprises an adder and a pseudo-random noise generator, the addition of said adder being controlled by said psuedo-random generator.
6. A synthesizer according to Claim 5 wherein said adder adds together said first signal and said second signal, said synthesizer further comprising timing means for coupling said first and said second signals from said storage means at a predetermined rate to produce a frequency of said tone-like signal proportional to the magnitude of said first signal.
7. A synthesizer according to Claim 5 wherein said first signal and said second signal are digitally formated.
8. A synthesizer of a set of tone-like signals of broadened bandwidth comprising:
first and second storage means storing respectively first and second signals each of which represents a magnitude of frequency;
means for combining said first and said second signals to provide a combined signal;
timing means coupled to said first and said second storage means for repetitively coupling said first signal and said second signal at a predetermined rate to said combining means;
noise generator means coupled to said timing means and said combining means for activating said combining means to produce a substantially random sequence of sums and differences of said first and said second signals;
means for integrating said combined signal to produce an integrated signal representing a phase;
means for converting said integrated signal to a tone-like signal; and means for scaling said tone-like signal.
first and second storage means storing respectively first and second signals each of which represents a magnitude of frequency;
means for combining said first and said second signals to provide a combined signal;
timing means coupled to said first and said second storage means for repetitively coupling said first signal and said second signal at a predetermined rate to said combining means;
noise generator means coupled to said timing means and said combining means for activating said combining means to produce a substantially random sequence of sums and differences of said first and said second signals;
means for integrating said combined signal to produce an integrated signal representing a phase;
means for converting said integrated signal to a tone-like signal; and means for scaling said tone-like signal.
9. A synthesizer according to Claim 8 wherein said timing means further comprises addressing means for sequentially addressing said first and second storage means to couple a set of first signals and a set of second signals to said combining means for producing a set of tone-like signals.
10. A synthesizer according to Claim 9 further comprising means for summing said tone-like signals to produce a composite signal having the form of a set of tone-like signals.
11. A synthesizer according to Claim 10 wherein said scaling means includes a memory, said synthesizer further comprising a third storage means storing signals representative of phase, said addressing means being coupled to said memory and to said third storage means for applying individual phase offsets and individual amplitude scale factors respectively to individual ones of said tone-like signals;
said timing means further comprising means for programming the addressing of said first, second and third storage means and said memory for altering the frequency, the phase and the amplitude of respective ones of said tone-like signals during successive intervals of time; and speaker means coupled to said summing means for converting said composite signal to an audible sound.
said timing means further comprising means for programming the addressing of said first, second and third storage means and said memory for altering the frequency, the phase and the amplitude of respective ones of said tone-like signals during successive intervals of time; and speaker means coupled to said summing means for converting said composite signal to an audible sound.
12. A synthesizer according to Claim 10 further comprising means for displaying broadened spectral lines of said composite signal.
13. In combination:
means for storing first and second signals;
means responsive to an input signal for generating a tone-like signal having a frequency proportional to said input signal;
means for directly coupling said first signal from said storing means to said generating means to provide a frequency of said tone-like signal proportional to said first signal; and wherein said coupling means includes means for randomly combining said second signal with said first signal to provide said input signal, said second signal introducing a broadened spectrum to said tone-like signal.
means for storing first and second signals;
means responsive to an input signal for generating a tone-like signal having a frequency proportional to said input signal;
means for directly coupling said first signal from said storing means to said generating means to provide a frequency of said tone-like signal proportional to said first signal; and wherein said coupling means includes means for randomly combining said second signal with said first signal to provide said input signal, said second signal introducing a broadened spectrum to said tone-like signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US92513078A | 1978-07-17 | 1978-07-17 | |
| US925,130 | 1978-07-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114954A true CA1114954A (en) | 1981-12-22 |
Family
ID=25451267
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA330,178A Expired CA1114954A (en) | 1978-07-17 | 1979-06-20 | Digital sound synthesizer |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1114954A (en) |
| DE (1) | DE2928896C2 (en) |
| ES (1) | ES482471A1 (en) |
| FR (1) | FR2431744A1 (en) |
| IT (1) | IT1120477B (en) |
| NO (1) | NO151802C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10787119B2 (en) | 2017-06-01 | 2020-09-29 | Audi Ag | Method for generating driving noises, acoustics controller and motor vehicle |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3697699A (en) * | 1969-10-22 | 1972-10-10 | Ltv Electrosystems Inc | Digital speech signal synthesizer |
| DE2507272A1 (en) * | 1975-02-20 | 1976-09-02 | Krupp Gmbh | METHOD FOR ELECTRONIC SIMULATION OF SHIP NOISE |
| IT1033400B (en) * | 1975-03-04 | 1979-07-10 | Contraves Italiana Spa | ELECTRONIC SIMULATOR OF PERIODIC SOUNDS OR NOISES WITH THE USE OF DIGITAL ELECTRONIC MEMORY ORGANS |
-
1979
- 1979-06-20 CA CA330,178A patent/CA1114954A/en not_active Expired
- 1979-07-06 IT IT49680/79A patent/IT1120477B/en active
- 1979-07-11 FR FR7917982A patent/FR2431744A1/en active Granted
- 1979-07-13 ES ES482471A patent/ES482471A1/en not_active Expired
- 1979-07-16 NO NO792361A patent/NO151802C/en unknown
- 1979-07-17 DE DE2928896A patent/DE2928896C2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10787119B2 (en) | 2017-06-01 | 2020-09-29 | Audi Ag | Method for generating driving noises, acoustics controller and motor vehicle |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2431744A1 (en) | 1980-02-15 |
| IT7949680A0 (en) | 1979-07-06 |
| NO151802C (en) | 1985-06-05 |
| NO151802B (en) | 1985-02-25 |
| ES482471A1 (en) | 1980-02-16 |
| DE2928896A1 (en) | 1980-02-07 |
| FR2431744B1 (en) | 1983-12-02 |
| DE2928896C2 (en) | 1984-03-15 |
| NO792361L (en) | 1980-01-18 |
| IT1120477B (en) | 1986-03-26 |
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