US2995707A - Frequency detector - Google Patents

Frequency detector Download PDF

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Publication number
US2995707A
US2995707A US764073A US76407358A US2995707A US 2995707 A US2995707 A US 2995707A US 764073 A US764073 A US 764073A US 76407358 A US76407358 A US 76407358A US 2995707 A US2995707 A US 2995707A
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Prior art keywords
frequency
output
voltage
amplitude
ratio
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Expired - Lifetime
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US764073A
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English (en)
Inventor
Jager Frank De
Petrus Josephus Van Gerwen
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/08—Measuring resistance by measuring both voltage and current
    • G01R27/10—Measuring resistance by measuring both voltage and current using two-coil or crossed-coil instruments forming quotient
    • G01R27/12—Measuring resistance by measuring both voltage and current using two-coil or crossed-coil instruments forming quotient using hand generators, e.g. meggers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00

Definitions

  • This invention relates to a frequency detector for detecting the variation of a characteristic speech frequency lying within a speech sub-band, the speech sub-band selected by means of a filter beng supplied to the input of the frequency detector.
  • t is of importance to know these characteristic speech frequencies, the socalled formant frequencies, which are determined by the resonant frequencies of the resonant cavities in the oral and nasal cavities and in the pharynx, and the so-called fundamental frequency, which is determined by the vibration frequency of the vocal cords.
  • FIG. 1a is a time diagram showing the variation of the oscillations associated with three letter sounds in the formant range from 800 c./s. to 2000 c./s.
  • the output voltage of the frequency detector is adversely afiected in a high degree and this phenomenon is due to the fact that at these instants the variation of the oscillations produced has -an uneven nature while the noise and interference voltages whch occur at these instants exert a comparatively great influence.
  • the output voltage of the frequency detector abrupt amplitude variations occur owing to the fact that the frequency detector invariably adjusts itself to the frequency component having the largest amplitude similarly to what takes place when a number of frequency-modulated oscillations of difierent strengths are received simultaneously.
  • the selected speech subband is supplied on the one hand to a network connected in a first chanel whch difierentiates signal frequencies and is succeeded by a rectifier with an associated low-pass filter, and on the other hand to a rectifier with an assocated low-pass filter which are connected in a second channel, the frequency detector also containing a ratio meter which is controlled by the output voltages of the two channels and is used for determining the ratio of the "ice output voltage of the first channel to the output voltage of the second channel, the output voltage of the frequency detector beng taken from the output circuit of the ratio meter.
  • FIG. 1 shows a number of wave forms illustrating the frequency detector in accordance with the invention
  • FIG. 2 is a block-schematic diagram of the frequency detector in acco-rdance with the invention
  • FIG. 3 is a frequency-voltage diagram illustrating the operation of the frequency detector in accordance with the invention.
  • FIG. 4 shows in detail the circuit arrangement of an embodiment of a ratio meter for use in a frequency detector in accordance with the inventin, while FIG. 5 shows a preferred embodiment of such a ratio meter.
  • the speech signals are derived from a microphone 1 and subsequently, after amplitude equalization in a ditferentiating network 2, amplified in a low-frequency amplifier, 3.
  • a band-pass filter 4 connected to the output circuit of the low-frequency amplifier 3 the oscillations U (t) situated in the formant range from 800 c./s. to 2000 c./s. are selected, whch oscillations may have the variation shown in FIG. 1a.
  • the oscillations U(t) selected by the band-pass filter 4 are supplied to a frequency detector 5 which is provided with two channels 6 and 7 connected in parallel to the band-pass filter 4.
  • the signal U(t) is difierentiated in a differentiating network 8, whch may comprise a series capacitance and a parallel resistance and has a time constant of about 10 seconds, so that a signal S(t) is produced the amplitude of which is proportional to the amplitude of the original sgnal U(t) multiplied by the instantaneous frequency w.
  • the variation of the dfierentiated signal S(t) is illustrated in FIG. 1b.
  • the differentated sgnalS(t) is supplied to a rectifier 9 with an associated low-pass filter 10, whch may comprise a series-resistance and a parallelcapacitance, while in the channel 7 the original signal U (t) is likewise supplied to a rectifier 11 with an associated low-pass filter 12, this rectifier circuit 11, 12 beng designed sirm'larly to the rectifier circuit 9, 10.
  • the cut-off frequencies of the low-pass filters 10, 12 are chosen so that during the intervals between the letter sounds an output voltage is also produccd at the output of the low-pass filters 10 and 12, these cutol frequencies beng situated, for example, between 10 c./s. and 50 c./s. and beng about 30 c./s.
  • FIGURES lc and 1d the broken lines show the envel0pes of the oscillations of FIGURES 1a and 1b, the voltages whch are produced at the output circuits of the low-pass filters 10 and 12 beng indicated by the solid curves.
  • the output voltages of the lowpass filters 10 and 12 control a ratio meter 13 the desired variation of the formant frequency, whch is illustrated in FIG. 1e, beng -achieved by determining the ratio between the output voltages of channels of an adjustable attenuator 14 connected in the channel 7 S as to precede the rectifier 11.
  • the frequency detector describedthere are produced by re'ctification in the rectfiers 9 and 11 and by the subsequent srnootln'ng in the low-pass filters 10 and 12 at the output circuits of these low pass filters 10 and 12 voltages which are equal to the smoothed values of the voltages set up at the outputs of the rectifiers 9 and 11.
  • I-f the amplitude of the input voltage of the rectifier 11 is a(t) at a certain instant
  • the input voltage of the rectifier 9 is proportional to the product of the amplitude a(t) and of the i11stantaneous frequency, as has been mentioned hereinbefore, so that in mathematical form the output voltages of the low-pass filters 12 and 10 can be represented by the values of the time integrals:
  • the output voltage of the frequency detector is determined substantially by the frequencies of the oscillations during the maximum amplitude values of the letter sounds the frequences of which are found to correspond exactly to the be determined by supplyingeach of these direct voltages to an amplifier having a logarithmic amplification characteristic, the output voltages of these amplifiers being compared in a dilerential network so that at the output of this network a voltage is produced which is proportional to the logarithm of the output voltage of the low-pass filter 10 less the logarithm of the output voltage of the low-pass filter 12.
  • a voltage is produced which is proportional to the loganthm of the ratio between the output voltages of the low-pass filters 10 and 12, the reqnired ratio being obtained by supplying the output voltage of the diierential network to an amplifier having an 6X ponential amplification characteristic.
  • the output direct voltages of the low-pass filters 10 and 12 in the channels 6 -arid 7 control amplitude modulators 15 and 16, which may be push-pull modulators, with associated output filters 19 and and carrier-wave oscillators 17 and 18 the frequencies f and f of which are 32 kc./s. and 48 kc./s., respectively.
  • the ratio meter to he employed will be described more fully hereinafter with reference to FIGURES '4and 5.
  • the ratio meter 13 provides a maan output voltage by only providing that in this event the carrier-wave oscillations f and f of the oscillators 17 and 18 are set up at the input of the ratio meter 13 in a suitable strength ratio.
  • the present embodirnnt the output circuits of the carrierwave oscillators 17 and 18 arecoimected, through adjustable attenuators 21 and 22, to the outputs of the output filters 19 and 20, respectively, provision being made by suitable adjustment of the attenuators 21 and 22 that in the absence of a speech signal the ratio meter 33 supplies an output voltage which corresponds to a frequency situated in abut the middle portion of the formant range concerned.
  • Such an adjustnient also provides the advantage that when a speech signal occurs aftera speech interval, the frequency detector rapidly adjusts itself to the desired value.
  • FIG. 3 shows a voltage diagram of the frequency detector shown in block-schematic form in FIG. 2, the output voltage V of the frequency detector being plotted as a function of the input voltage V at various frequencies of the input voltage.
  • the curves shown represent the variation of the output voltage V of the frequency detector as a function of the input voltage V at frequencies of 800 c./s., 1400 c./s. and 2000 c./s. respectively.
  • FIG. 4 shows in detail the circuit arrangement of a ratio meter for use with the frequency detector shown in jpentode 25, there being also applied to this/control grid through a resistr 26 the alternating voltage f which is derived from the channel 7 and the amplitudeof which is deterrhined by the rectified input signal.
  • the anode ciicuit of the pentode 25 contains two parallel-connected restrs 27, 28, there being connected to a tapping on the1esistor 27 a selecting filter 29 tuned to thefi'equeny -f2 and to a rived from the filter 29 is rectified by a rectifier 32 to which a bias voltage is applied which is supplied by a potentiometer 31 connected between the positive voltage terminal and earth, the negative direct voltage obtained being supplied, through a resistor 34, to the control grid of the pentode 25 tot slope control.
  • the oscillation at frequency f selected by the filter 30 is rectified in a rectifier circuit comprising a rectifier 35 and an output impedance 36 and subsequently is supplied, through a low-pass filter 37, to output terminals 38, 39, the direct voltage taken from the terminals 38, 39 being the output voltage of the ratio meter.”
  • the use of the slope control ensures that the oscillations at frequency f are amplified in the pentode 25 in inverse proportion to the amplitude of the oscillation f supplied to the input of the pentode 25, so that the voltage taken from the terminals 38, 39 is proportional to the amplitude ratio between the output voltages of channels 6 and 7.
  • the output voltages of the channels 6 and 7 are supplied through series-resistors 40 and 41 and a grid capacitor 42 to the control grid of a pentode 43, the amplitude ratio being determined, however, by amplitude lmitation instead of by slope control.
  • a resonant circuit 44 which passes the oscillations and an amplitude limiter comprising two rectifiers 45, 46 connected with asymmetric conductivty with respect to each other, there being connected to the output circuit of the limiting arrangement a resonant circuit 47 which passes the oscillations and f While the junction of the rectifiers 45, 46 is connected to the junction of a potentiorneter 49, 50 which is connected between the positive voltage terminal 48 of the voltage supply source and earth and supplied a current in the pass direction of the rectifiers 45, 46.
  • the rectifier 45 is cut oi, while a constant current flows through the resistor 49 of the potentiometer 49, 50, which is made comparatively large, and through the rectifier 46 to the output impedance 47, while conversely, when the output voltage of the pentode 43 is lower than the voltage at the junction of the rectifiers 45, 46, the rectifier 45 is conductive and the rectifier 46 is cut ol so that no current flows to the output impedance 47.
  • the limiter is proportioned so -as to provide complete lmitation already at signals of small amplitude.
  • the output voltage of the limiter circuit is supplied for amplification to a pentode 51, the oscillation f being selected by means of a selecting filter 52 connected in the output circuit of the pentode 51 and providing the output voltage of the frequency detector after rectification in a rectifier stage comprising a rectifier 53 and an output impedance 54 and subsequent smoothing in a low-pass filter 55.
  • the output voltage of the frequency detector is taken from output terminals 56, 57.
  • the amplitude of the oscillation f is made smaller than the amplitude of the oscillation by a factor of, for example, 4 to 5. It should be remarked here that in the output circuit of the limiter in'stead of the oscillation at frequency f use can also be made of the image frequency of f with respect to 2, which consequently has a frequency of 2f -f
  • the ratio meters described hereinbefore can obviously be replaced by other ratio meters.
  • the output voltages of the low-pass filters in the channels 6 and 7 may be converted into alternating voltages of equal frequencies the output alternating voltage of the channel 6 being subsequently shifted in phase and added to the alternating voltage of the channel 7.
  • the phase of the sum voltage obtained varies in accordance with the amplitude ratio between the output voltage of channel 6 and the output voltage of channel 7 so that the desired ratio is obtained by phase measurement.
  • the frequency detector described can also be used for the detection of the variation of the fundamental frequency, for which purpose a suitable speech sub-band containing the fundamental frequency is supplied to the input of the frequency detector.
  • This speech sub-band can be selected directly from the speech signal or it can be obtaned by means of amplitude detection of preferably at least one higher formant range.
  • a frequency detector for the detection of the variation of a characteristic speech frequency situated within a speech sub-band comprising first and second channels having input and output terminals, means applying signals of said sub-band to the input terminals of said first and second ohannels said first channel comprising in the order named serially connected difierentiating means, first recti dier means, first low-pass filter means, and modulator means, said second channel comprising in the order named serially connected second rectifier means, second lowpass filter means, and second modulator means, ratio meter means connected to said output terminals to provide an output signal that is a function of the ratio of the output voltages of said first and second channels, and oscillator means connected to said first and second modulator means.
  • the frequency detector of claim 1 comprising means for adjusting the outputs of said first and second modulator means so that an output signal trom said ratio meter means occurs in the absence of said signals of said sub-band.
  • a frequency detector comprising a source of input signals, first and second channels having input and output terminals, means applying said signals to said input terminals, said first channel comprising in the order named serially connected diiferentiating means, rectifier means, lowpass filter means, and first modulator means, said second channel comprising in the order named serially connected rectifier means, low-pass filter means, and second modulator means, first and second oscillator means having difierent frequency oscillations connected respectively to said first and second modulator means whereby said oscillations -are modulated by the signals in their respective channels, and ratio meter means connected to said output terminals to provide an output signal that is a function of the ratio of the output voltages of said first and second ol1annels.
  • said ratio meter means comprises an amplifier device having an input 'electrode and an output electrode, said output terminals being conneoted to said input electrode, a first output filter tuned to the frequency of oue of s"aid oscillator means, rectifier means c'onneted betweei1 said input eleotrode and said first output filter, and a second output filter tuned to the frequency of the other of said oscillator means and being connected between said output eleotrode and an output circuit.
  • said ratio meter means compriss lmiter means having an input circuit connected to said output terminals and an output circuit cofinected to cfreqency seleotive filter means tuned to the frequency of one of said oscilltor means, the amplitude of the output voltage of the (me -cha'nnel comprsing said one oscillator means being less than the output voltage of the other channel.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Human Computer Interaction (AREA)
  • Signal Processing (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Computational Linguistics (AREA)
  • Measurement Of Current Or Voltage (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
  • Measuring Frequencies, Analyzing Spectra (AREA)
US764073A 1957-10-14 1958-09-29 Frequency detector Expired - Lifetime US2995707A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL221597A NL97484C (nl) 1957-10-14 1957-10-14 Frequentiedetector voor het bepalen van de karakteristieke frequentie van een binnen een een zekere gespreksband optredende trilling

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US2995707A true US2995707A (en) 1961-08-08

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US (1) US2995707A (esLanguage)
JP (1) JPS368093B1 (esLanguage)
DE (1) DE1151284B (esLanguage)
FR (1) FR1212914A (esLanguage)
GB (1) GB844561A (esLanguage)
NL (1) NL97484C (esLanguage)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11114979B2 (en) * 2018-12-11 2021-09-07 Silicon Integrated Systems Corp. Frequency detector

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2323108C2 (de) * 1970-12-18 1983-01-20 Siemens AG, 1000 Berlin und 8000 München Verfahren zur Ermittlung der Grundfrequenz eines wenigstens zeitweise periodischen Signals
JPS5129860A (en) * 1974-09-06 1976-03-13 Matsushita Electric Industrial Co Ltd Fmmam henkanki
DE3690169C2 (esLanguage) * 1985-04-10 1990-10-04 Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka, Jp

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2418284A (en) * 1943-04-24 1947-04-01 Bendix Aviat Corp Differential voltage measuring circuit
US2541067A (en) * 1944-11-30 1951-02-13 Sperry Corp Frequency responsive device
US2576249A (en) * 1947-08-28 1951-11-27 Bell Telephone Labor Inc Level ratio measuring system
US2711516A (en) * 1949-10-29 1955-06-21 Rca Corp Frequency discriminatory systems
GB788565A (en) * 1954-08-11 1958-01-02 Gen Electric Improvements in and relating to frequency response determining apparatus
US2857465A (en) * 1955-11-21 1958-10-21 Bell Telephone Labor Inc Vocoder transmission system
US2896161A (en) * 1942-06-30 1959-07-21 Bessie E Fox Measuring system

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896161A (en) * 1942-06-30 1959-07-21 Bessie E Fox Measuring system
US2418284A (en) * 1943-04-24 1947-04-01 Bendix Aviat Corp Differential voltage measuring circuit
US2541067A (en) * 1944-11-30 1951-02-13 Sperry Corp Frequency responsive device
US2576249A (en) * 1947-08-28 1951-11-27 Bell Telephone Labor Inc Level ratio measuring system
US2711516A (en) * 1949-10-29 1955-06-21 Rca Corp Frequency discriminatory systems
GB788565A (en) * 1954-08-11 1958-01-02 Gen Electric Improvements in and relating to frequency response determining apparatus
US2857465A (en) * 1955-11-21 1958-10-21 Bell Telephone Labor Inc Vocoder transmission system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11114979B2 (en) * 2018-12-11 2021-09-07 Silicon Integrated Systems Corp. Frequency detector

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DE1151284B (de) 1963-07-11
NL97484C (nl) 1961-03-15
GB844561A (en) 1960-08-17
FR1212914A (fr) 1960-03-28
JPS368093B1 (esLanguage) 1961-06-20

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