DE2444402A1 - SYSTEM FOR COMPARING THE FREQUENCIES OF PREFERABLY TWO TONE FREQUENCY SIGNALS - Google Patents

Description

PATENT LAWYERS

DIPL.-ING. LEO FLEUCHAUS

DR.-ING. HANS LEYH

Dipl. -Ing. Ernst Rathmann

Munich 71, September 17, 1974 Melchloretr. 42

Our reference: MO164P-1213

Motorola, Inc.

5725 East River Road

Chicago, Illinois 60631

United States

System for comparing the frequencies of preferably
two audio frequency signals

The invention relates to a system for comparing the frequencies of preferably two audio frequency signals with means for deriving a first alternating current signal as a function of one first audio frequency signal and a second alternating current signal in dependence on a second audio frequency signal.

There are a variety of use cases where it is necessary is to compare the frequency of different signals with each other. A significant use case arises in the coordination electronic musical instruments, where it becomes necessary to accurately compare the frequencies of different tones. Various methods and techniques are known to

Fs / mÜ 509812/0868 like

MO164P-1213

to be able to make similar frequency comparisons and frequency determinations. One common system uses reed relays that operate on the individual frequencies are matched, after which a Audio frequency signal that tongue is set into vibration, the resonance frequency of which is equal to the applied frequency. With another System, the frequency of a tone is compared with the known frequency of an oscillator and e.g. with the help of a cathode ray tube Frequency comparison made with the help of Lissajous' figures.

Such systems are relatively complex and allow an exact frequency comparison only at discrete points, with none direct frequency comparison between two signals is possible. A direct comparison is likely with the help of the Lissajous' schan figures possible, but these figures are difficult to interpret unless the ratio of the frequencies of the applied signals is an integer is. One interpretation of the Lissajous' see figures is special Difficult at frequencies that are assigned to the tones of a scale, when namely to determine broken frequency ratios are.

The invention is based on the object of providing a system for frequency comparison with visual display, with which it is preferably it is possible to tune electrical musical instruments by comparing frequencies. A frequency comparison should also be possible be between signals whose frequencies do not form an integer ratio. This frequency comparison system should be as simple as possible and inexpensive to manufacture and easy to use even by non-specialists.

This object is achieved according to the invention in that the devices for deriving the alternating current signals are coupled to a display device via a pattern generator that with the display

- 2 - device

509812/0868

MO164P-1213

device a high-frequency sampling circuit and a low-frequency Scanning circuit are coupled, which by a horizontal and a vertical scanning a grid on the screen of the display device generate signals representative of the first and second AC signals alternately by the pattern generator to the display device, and that the high frequency sampling circuit is coupled to the pattern generator such that the representative signals alternately applied to the display device are only effective for part of the high-frequency sampling cycle and cause the display of a bar pattern, in which the number and position of the bars shown the frequency and phase position of the first and second AC signals are proportional.

Further features and refinements of the invention are the subject matter of further claims.

A particularly advantageous embodiment of the invention uses a video monitor with a divided screen. With the help of a pattern generator, a bar pattern is created for the frequency of the individual signals to be compared, the distance between the individual bars or the number of bars displayed on the screen characterizing the frequency and the position of the bars characterizing the phase position. The vertical scanning circuit of the monitor is synchronized to the frequency of the one audio frequency signal, which means that the bar pattern assigned to this frequency is displayed in a stationary manner on a part of the screen. The frequency of the signal shown on the other part of the image is determined with the fixed signal by comparing the numbers of the bars on the screen and their position or displacement with respect to the fixed bar pattern.

Advantages and features of the invention also result from the

- 3 - following

509312/0868

K ΜΟ164Ρ-1213

following description of an embodiment in conjunction with the claims and the drawing. Show it:

Fig. 1 is a block diagram of a frequency comparison circuit with visual display according to the invention;

Fig. 2 is a schematic circuit diagram of the display according to the invention;

up to 6 line patterns on one screen, as they are different Resulting frequency ratios for the applied signals.

In Fig. 1, a part of a musical instrument is shown, the oscillators and dividers 10 and 20 and associated keyboards 12 and 22 respectively. An amplifier 14 or 24 is connected to the keyboard 12 or 22 and on the output side to a pattern generator 16 connected. This pattern generator 16 is connected to display devices, e.g. in the form of a video monitor 18, and generates bar patterns on first and second portions 26 and 28, respectively, of a split screen. At the same time on the monitor 18 a vertical synchronization voltage is applied from the pattern generator 16, while the horizontal synchronization is applied from the monitor 18 is effective on the pattern generator 16.

In operation, the actuation of the keyboard 12 produces a first tone transmitted from the oscillators and dividers 10 to the amplifier 14. The signal amplified by the amplifier 14 is generated in the pattern generator processed to a video signal of substantially in the form of a square wave with the same frequency as that of the first tone to the

- 4 - monitor

609812/0868

.5.

MO164P-1213 '

Apply monitor 18 and generate a bar pattern in part 26. In the same way, the oscillators and dividers 20 are turned on The signal is transmitted via the keyboard 22 to the amplifier 24 which, after being amplified in the pattern generator 16, generates a video signal, which is shown in the form of a bar pattern in part 28 of the screen. To synchronize the vertical scanning a vertical sync signal is applied to monitor 18 to adjust the vertical scan to a sub-frequency of that from amplifier 14 to synchronize the supplied signal. The horizontal synchronization signal is from the horizontal synchronization circuit of the monitor 18 derived and controls a gate circuit in the pattern generator 16 to alternate signals via the amplifier 14 and the amplifier to be transmitted to the video part of the monitor 18, so that corresponding bar patterns in the parts 26 and 28 of the screen for display reach.

In Fig. 2 is the circuit diagram of an embodiment of the pattern generator 16 in connection with the block diagram of a video monitor 18. The output of the amplifier 14 is connected to an input terminal 34 of the pattern generator 16. This input terminal 34 is also connected to the base of a transistor 36 through a capacitor 38 and a resistor 40. There is an input terminal accordingly 44 with the output of the amplifier 24 in connection and is at the base of a transistor 46 via a capacitor 48 and a resistor 50. The collectors of transistors 36 and 46 are connected to a power supply A + via resistors 42 and 52, respectively, and at the same time via resistors 63 and 64 at the input of a video amplifier 60 in the monitor 18. The collector of the transistor 36 is also connected to the Vertical oscillator 54 connected. The collectors of two transistors and 72, like the emitters of these transistors, are connected to the collectors or emitters of transistors 36 and 46, the emitters of the

- 5 - transistors

50981 2 / Ü868

MO164P-1213

Transistors are each connected to ground potential or a common reference potential. The base of transistor 62 is through a Resistor 68 is connected to the collectors of transistors 64 and 66 which are connected to ground via interconnected emitters. Corresponding the base of the transistor 72 is connected via a resistor 78 to the collectors of two transistors 74 urid 76, whose Emitter are also connected together to ground. The collectors' of the transistors 74 and 76 are connected to the power supply via a resistor 79 A +, which also applies to the transistors 64 and 66, which are connected to the power supply A + via a resistor 69. Furthermore, the collectors of these transistors 74 and 76 are connected to the base of the transistors 74 and 76. The base of transistors 64 and 66 is connected to the output of horizontal oscillator 90 in monitor 18 via resistors 84 and 86 and a capacitor 88 are connected. A resistor 87 is dimensioned in its size in such a way that the division of the screen into the center of the image grid.

The output of the horizontal oscillator 90 is also, on the one hand, to a horizontal deflection circuit 92, which is the horizontal deflection coil drives into a deflection unit 94, and connected to a high voltage circuit 96 which is connected to the anode of a display device in the form of a picture tube 98 is connected. A vertical output circuit 100 of the monitor 18 is on the input side with the Vertical oscillator 54 and connected on the output side to the vertical deflection coil in deflection unit 94. The output of the video amplifier 60 lies on the grid 102 of the cathode picture tube 98 in order to modulate the raster that is displayed on the screen of this picture tube the horizontal output circuit 92 and the vertical output circuit 100 are generated.

In operation, an audio signal is applied to the input terminal 34

- 6 - through ...

509812/0868

MO164P-1213

amplified by transistor 36 and limited in terms of amplitudes, so that a substantially square wave is available at the input of amplifier 60 when the transistor is not made conductive. Accordingly, the transistor 46 amplifies the signals applied to the input terminal 44 and transmits them to the amplifier 60 when the transistor 72 'is not conductive. the Transistors 62 and 72 serve the purpose of deriving the signals on the corresponding transistors 36 and 46 to ground when either the Transistor 62 or transistor 72 is conductive.

The horizontal oscillator 90 provides oscillations with the relative high horizontal deflection frequency, which can be of the order of 15,750 Hz, to the horizontal output circuit 92, which applies a sawtooth voltage to the deflection unit 94, to to create the bar pattern on the screen of the cathode picture tube 98 by means of a horizontal scan. The return impulses from of the horizontal output circuit 92 are stepped up and limited to serve as the anode voltage in a conventional manner for the Cathode picture tube 98 to be available. The output signal of the horizontal oscillator 90 is via a capacitor 88 at the Base of transistors 64 and 66 effective, which are connected in parallel. Instead of the two transistors 64 and 66, a Find single transistor use, but the integrated design to be produced circuit preferably consists of four Doppelstuferi, of which the one with the transistors 64 and 66 is connected.

Since the horizontal oscillator 90 is capacitive to the transistors 64 and is coupled, both transistors are conductive when the value of the AC component of the signal from the horizontal oscillator 90 is sufficient, to bias both transistors in the forward state.

- 7 - Is

509612/0868

MO164P-1213

However, if the value of the AC component is less than that for the bias of the base-emitter path in the forward direction necessary value, then the two transistors 64 and 66 are made non-conductive. The output signal at the collectors of transistors 64 and 66 is, for this reason, substantially rectangular and has a Frequency equal to the frequency of the signal from the horizontal oscillator 90.

The square wave signal from transistors 64 and 66 goes to the base of the transistor 62 is applied to make this transistor conductive when the square wave assumes the highest level value, and on the other hand to make the transistor 62 non-conductive when the lowest level of the square wave is effective. The signal from the transistors 64 and 66 is also applied to the base of transistors 74 and 76, which are in the same configuration as transistors 64 and are constructed and act as a phase inversion stage to a second square wave that is 180 out of phase. The signal from the collectors of transistors 74 and 76 is sent to the base of the Transistor 72 applied to make this transistor conductive and non-conductive alternately when the transistor 62 accordingly not conductive or conductive .is.

Since the transistors 72 and 62 are alternately rendered conductive, becomes also alternately the signal applied to the transistors 46 and 36 is derived to ground, while the other signal of these transistors is applied to the video amplifier 60. This function sequence mentioned causes the electron beam of the cathode picture tube 98 through the Video amplifier 60 as a function of the signal from transistor 36 during the first part of the horizontal deflection and as a function is modulated by the signal from transistor 46 during the remainder of the horizontal deflection to achieve the split screen effect to effect.

- 8 - That

509812/0868

MO164P-1213

The signal from transistor 36 is also fed to vertical oscillator 54, in order to apply a synchronization pulse which causes the vertical oscillator to operate at a partial frequency of the frequency of the signal from Transistor 36 works. The vertical oscillator 54, which oscillates at a lower frequency than the horizontal oscillator 90, causes the vertical Output circuit 100 applies a sawtooth signal to the vertical deflection coil of deflection unit 94 and the electron beam in the cathode picture tube deflects in the vertical direction with a fraction of the frequency of one of the audio frequency signals applied to the frequency circuit. the Synchronization causes a series of stationary horizontal Bars corresponding to the tone frequency to which the system is synchronized. The number of bars is determined by the frequency ratio of the Audio frequency signal and the operating frequency of the vertical oscillator 54 is determined. The number of bars that appear on the screen for the other signal is determined by the frequency ratio that is results from the frequency of the signal and that of the vertical oscillator 54, whereby the frequency comparison between the two is sent to the frequency comparison circuit applied signals according to the invention results.

In Figure 3 the bar pattern is in parts 26 and 28 of the screen of the monitor 18 for the case that the frequencies to be compared are the same both in terms of frequency and phase. This results from the same number of bars in both parts 26 and 28 of the screen and from the fact that the bars are on the same horizontal plane.

In Fig. 4, the bar pattern is shown for the case that the two compared audio frequency signals have the same frequency, but are 180 ° out of phase with each other. This derives from the same distance between the bars in part 26 and 28 of the screen, while the phase shift by 180 from the uniform staggered arrangement of the bars in the two parts of the screen.

- 9 - Off

509812 / Ü868

244U02

MO164P-1213

From the illustration according to FIG. 5 it can be seen that the frequency ratio the signals applied to the comparison circuit behave as 2: 1. This can be deduced from the fact that the spacing of the bars in the area 28 is half as large as in the area 26 of the picture tube. Correspondingly, a frequency ratio can also be used for the illustration according to FIG. 6 Derive from 5: 4, since in part 28 of the screen there are five bars for every four bars in part 26 of the screen.

The visual display according to the invention is also for the comparison of Very useful signals that have only a small frequency shift from one another. Since the vertical deflection of the monitor 18 on the im Part 26 of the screen is synchronized with the signal shown, the bars in this part of the screen remain stationary. The bars in the Part 28 of the screen remain stationary when the frequency of the signal shown equals the frequency of the signal shown in part 26 has an integer ratio and is, for example, 1: 1, 2: 1 or 5: 4 in accordance with the representations according to FIGS. 3 to 6. If this relationship is not an integer, the bars in area 28 run through either upwards or downwards with respect to the bars in area 26. A run through the bar upwards indicates that the frequency is slightly higher, whereas a lower frequency is indicated by scrolling through the bars indicated below.

So shows z. B. traversing the bars in the area 28 according to FIG above that the frequency of the signal displayed in part 28 of the screen is slightly above the frequency of that in part 26 of the screen represented signal lies. Correspondingly, a downward passage through the bars in the area 28 according to FIG. 5 indicates / that the frequency ratio is slight is greater than 2: 1, whereas a passage through the bars in the area 28 upwards for the representation according to FIG. 6 indicates that the displayed frequency ratio is slightly greater than 5: 4. In this way, the frequency relationship between two signals can be very

- 10 times

509812/0868

2UU02

MO164P-1213

times by counting the bars in both sub-areas of the screen, whereby when scrolling through the bars, one side can be deduced that the frequency ratio shown is not exactly an integer.

The frequency comparison circuit according to the invention with associated Visual display offers the great advantage that a frequency comparison is possible in a simple manner with a very precise display, this comparison circuit can be used particularly advantageously when tuning musical instruments.

Although in the preceding description a visual display with horizontal lying beam was explained, it is obvious that a Representation with vertical bars is possible if the picture tube is rotated by 90. This is how the horizontal oscillator works instead of the vertical oscillator on a sub-frequency of the frequency of the one applied tone. It can also be used instead of a cathode picture tube Solid-state display devices are used, which can be controlled with a corresponding synchronization to the desired Trigger display. By designing the circuit accordingly the frequencies of three different ones can also be shown on the screen Compare audio frequency signals by dividing the screen into three parts.

- 11 - Claims

5098 12/0868

Claims (4)

MO164P-1213 Patent Claims 1. J system for comparing the frequencies of preferably two audio frequency signals with means for deriving a first alternating current signal as a function of a first audio frequency signal and a second alternating current signal as a function of a second audio frequency signal, characterized in that the means (14, 24) for deriving the AC signals are coupled to a display device (18) via a pattern generator (16) that with the display device (18) a high-frequency scanning circuit (90, 92) and a low-frequency scanning circuit (54, 100) are coupled, which by a horizontal and a vertical Scanning generate a raster on the screen of the display device, that the pattern generator (16) for the first and second AC signals alternately applies signals representative of the display device, and that the high-frequency scanning circuit is coupled to the pattern generator in such a way that the alternately to the display device Attention applied representative signals are only effective for part of the time of the high-frequency sampling cycle and cause the display of a bar pattern in which the number and position of the bars shown are proportional to the frequency and phase position of the first and second alternating current signals. 2. System according to claim 1, characterized in that the low frequency sampling circuit (54, 100) with the first device (14) is connected to derive a first alternating current signal and, depending on the first alternating current signal, the operating $ 0981 2/0868 »Η. 244U02 ΜΟ164Ρ-1213 frequency of the low-frequency sampling circuit synchronized to a fraction of the frequency of the first audio frequency signal. 3. System according to claim 2, characterized in that the Means (14, 24) for deriving the alternating current signals comprises limiting amplifiers which are substantially square-shaped Supply alternating current signals. 4. System according to one of claims 1 to 3, characterized in that a video amplifier (60) is present to the with the help of the horizontal and vertical scanning circuit to modulate the raster generated, and that the video amplifier with the pattern generator (16) and the display device (18) is coupled in such a way that the grid is dependent on the first and second alternating current signals can be modulated. 50981 2/0868