DE2939962A1 - Time compression expansion of tape recorded speech - using variable ratios selected by operator and avoiding speech distortion by accurate matching - Google Patents

Abstract

A magnetic tape recording system of use in conferences, language studies etc., allows direct operator control of the feedback rate without distortion of the replayed speech. The system has a magnetic tape drive system with a replay pick up head coupled to an amplifier. The time axis compression-expansion stage allows for compression-exansion ratios of 0.3, .5 to 2.0. The compression-expansion stage is controlled by a switching unit that is connected to the power drive elements of the magnetic tape recorder. A potentiometer and selector switches from the basis of the switching unit that allows the motor speed and appropriate compression-expansion ratio to be selected.

Description

Timeline compression / expansion device

for audio signals The invention relates to an improved time axis compression / expansion device, hereinafter also referred to as a compander device for audio signals.

Magnetic tape recorders are often used for the production of e.g.

Conference protocols or to record the conference presentations Repeated listening to the magnetic tape, used for language training, etc. Included However, from the point of view of an economical way of working, various the disadvantages listed below are highlighted. When preparing minutes of the conference or when studying language the tape recorder must be switched off from time to time, because the speed of the reproduced speech affects the writing speed of the listener exceeds. If the recording is also listened to via the tape device as much time is required for this as for the recording. This leaves but perform more economically if, for example the Motor drive of the magnetic tape recorder to slow down or accelerate the playback speed could be set. Although in this way the speed of speech reproduction could be changed to the value suitable for the intended purpose this changes the pitch (pitches) of the speech signals and thus their intelligibility degraded so much that the language becomes difficult to understand. For this reason There is a need for a device that can help improve playback speed can be changed without changing the pitch of the speech at the same time. This requirement has so far been met with the rotating magnetic head system, which voice signals treated or processed as analog signals, i.e.

without analog / digital or A / D conversion, or with a device the analog or digital storage elements for adjusting the pitches by changing them the speed for changing addresses used for writing and reading. However, these previous devices are so complex or

complicated in structure that they are very expensive.

The previous devices that meet the requirement mentioned are provided with two working or operating sections, of which the one changes the compression / expansion or compander ratio and the other toggles the timeline compander function on and off. For switching the compander ratio two systems have already been proposed, namely the continuous adjustment system and the gradual adjustment system for this ratio. The processing however, of audio signals through a time axis compander device has inevitably result in a sound output of reduced quality, because, for example, when transmitting between the memory elements the waveform is distorted by A / D or D / A conversion Noise is introduced and the discontinuity at signal connection sections (signal connecting sections) also results in noise. If on the other hand the audio signals without time axis compander processing, only a change in playback speed are subjected, it is shown in tests that although the audio frequency height by changing the timbre (tone) is changed, the intelligibility of the reproduced audio signals remains unaffected as long as there is only a slight difference between the playback speed and the original recording speed.

In addition, with the previous devices to change the speed of the reproduced sound signals by hand, a setting knob on the setting operating part be operated, which proves to be so cumbersome and laborious that this causes the Job performance in the preparation of machine or handwritten records is significantly affected after the magnetic tape recording.

The object of the invention is therefore in particular not to create a with these deficiencies, cost-saving timeline compander device for Sound signals through which the repeated eavesdropping on magnetic tapes for production of conference protocols, language training etc. is facilitated and with which A control unit is also offered that is particularly good for playback of sound signals with changed speed.

This object is characterized by what is stated in the attached claims Features solved.

The following are preferred embodiments of the invention the accompanying drawing explained in more detail. Show it: Fig. 1 a Block diagram of a device with features according to the invention, FIG. 2 is a circuit diagram of part of the apparatus of Fig. 1, Fig. 3 is a block diagram of another Embodiment of the device according to the invention, FIGS. 4A to 4K flow charts for various exemplary modes of operation, FIGS. 5 and 6 detailed circuit diagrams of part of the circuits of Fig. 3, Fig. 7 is a block diagram of still another Embodiment of the invention, FIG. 8 is a block diagram of an exemplary memory for the circuit according to FIG. 7, FIG. 9 is a block diagram of a further embodiment of the invention and FIG. 10 is a schematic representation to illustrate a another example of application of the invention.

The invention seeks to eliminate the disadvantages outlined at the outset in the first embodiment an operating or processing device which the timeline compander ratio changes or switches. In further embodiments are a compander device based on the equal or constant difference modulation system, another compander device residing in digital signal memory with a random memory is equipped and digitized audio signals with predetermined periods in the Memory and write these signals with different periods read out capable, or a foot-operated sound reproduction speed control device is provided, which is connectable to a time axis compander device and not just the audio signal playback speed to vary compared to the original audio signal speed, but also a conversion processing of the audio frequency levels of the reproduced signals for Ability to generate easily understandable sound information.

The embodiment of the invention shown in Fig. 1 comprises a Magnetic tape 1 for audio signal recording, a reproducing magnetic head for audio recording, a preamplifier 3 for amplifying that reproduced by the reproducing head 2 Signal to one for treatment or processing by time axis compression / expansion suitable level, also referred to below simply as a compander circuit Timeline Compression # stretching circuit that uses the one supplied by the preamplifier 3 Sound input signal compressed or compressed or stretched or expanded, one Loudspeaker 5, a compander ratio switching circuit 6, a drive 7 for the Magnetic tape 1 and a drive control circuit 8 for the drive 7.

The compander ratio switching circuit 6 of FIG. 1 is in FIG. 2 illustrated in detail. It consists of a slide resistor or potentiometer 9, slide switches 10 and 11 and a group of resistors 12, which between the switch 10 and the potentiometer 9 are switched on.

The potentiometer 9 interacts with the slide switches 1o and 11.

When the compander ratio is 1 or close to 1, the Arrangement according to FIGS. 1 and 2, on the one hand, via the slide switch 10, the potentiometer 9 so connected to the drive control circuit that the speed of the Magnetic tape 1 is continuously adjustable, while on the other hand via the slide switch 11 the audio signal from the preamplifier 3 bypassing the timeline compander circuit 4 is passed directly to the loudspeaker 5. With a different compander ratio (e.g. 0.3, 0.5, 0.7, 1.4, 1.7 and 2.0; see Fig. 2) is activated by means of the slide switch 10 from the group of resistors 12 of the set compander ratio corresponding resistor selected and connected to the drive control circuit 8, in order to set the required magnetic tape speed in this way. on the other hand the audio signal from the preamplifier 3 to the compander circuit is via the slide switch 11 4, so that the audio signal is sent to the loudspeaker 5 can be transferred.

There are modifications to the embodiment described above in adaptation to the actual circumstances or requirements possible, for example in the way that with such a device with extended possibilities, so that they change the playback speed, but not the timbre opposite can modify the original playback speed, the timeline compander processing the audio signals only occur before playback, if the device does not provide sufficient information capable of generating intelligible audio signals.

As can be seen from the above, with the invention has thus provided a high performance time axis compander apparatus as this Apparatus performing timeline compander processing in dependence of sizes for the compander ratio can be selected.

The second embodiment of the invention shown in FIG. 3 comprises a magnetic tape 22 for sound recording, a reproducing magnetic head 21, a preamplifier 23 for Amplification of the signals sampled by the playback head 21 to a suitable one Level for time axis processing, a constant difference -Modulator 24, which the output signal of the preamplifier 23 as an input signal of a constant difference modulation (Delta modulation) subject to random memories 25 and 26, which are dependent of clock pulse signals PT1 and PT2 from address counters 31 and 32 and read-write signals RW and RW from a control circuit 34 for writing digital data from the modulator 24 or to read out this stored data to a D / A converter via a gate circuit 27 serve, a low-pass filter 29, which high-frequency components of the analog data from D / A converter 28 filters out before output to output amplifier 36, one with the Output amplifier 35 connected speakers 36, pulse oscillators 30 and 33, the encoded pulses EPS or decoded pulses DPS for controlling the modulator 24 and the D / A converter 28 provide, and a compander ratio switching circuit 37 for changing the compander ratio for audio signals. This circuit works as follows: A change in the setting of the switching circuit 37 not only causes a change in the number of repetitions of address pulses APSA and APSB via the Control circuit, but also a change in both the modulation ratio of the modulator 24 as well as the tape speed of the tape recorder. The for Control circuit supplied output signals EPS and DPS from the pulse oscillators 30 and 33 supply read / write signals RW and RW with fixed and variable frequencies.

Although in the circuit described above as a memory Random memory is provided, this can of course also by means of a shift register be replaced.

The following is based on the clock control or flow chart according to Figure 4 illustrates the operation of the time axis compander apparatus with that described above Structure explained.

Fig. 4A illustrates a sound recording at normal tape speed preserved original resp.

Original signal. Fig. 4B shows a lower tape speed reproduced signal, for example when playing back at half tape speed and its frequency to half the frequency of the original signal has been reduced. This slowed playback signal is on electromagnetic Paths taken by the playback head 21 from the magnetic tape 22 via the preamplifier 23 to the constant difference modulator 24, an analog / digital or A / D conversion subject to the timing control of the encoded pulse EPS according to Fig. 4K, output by the pulse oscillator 30 and then according to the address counter 31 or 32 are written into addresses (memory locations) in the random memories 25 and 26. These two random memories 25 and 26 alternately repeat writing and reading processes in accordance with the read / write signal RW shown in FIG. 4F from the control circuit 34 and the read / write signal RW (Fig. 4G) with an opposite to the signal RW Phase. Simultaneously with this alternating repetitive procedure, the from the control circuit 24 output address pulses APSA and APSB (Figs. 4A and 41) are counted by the address counter 31 and 32, respectively, whereby the writing and reading speeds the random memories 25 and 26 can be controlled. In the assumed example with a Audio signal compander ratio of 1: 2 is the speed at which data is transmitted are read out from the random memories 25 and 26, twice as high as the writing speed into the random memories 25 and 26. The data read out from the latter are thus alternately supplied by the gate circuit 27 to the D / A converter 28, where they are in accordance or according to the timing of the decoded pulses DPS (Fig. 4J) from the pulse oscillator 33 can be converted into analog signals.

The signal played back at a slower speed according to Fig. 4B, the frequency of which is half the frequency of the original signal, is obtained thus after passing through the D / A converter 28 has the same frequency like the original signal (see Fig. 4C). This time expanded output signal is finally from the loudspeaker 36 via the low-pass filter 29 and the downstream Output amplifier 35 output as a sound signal.

As shown in Fig. 4C, each and every block of the original signal becomes twice repeated. This is because those generated by the frequency adjustment Blanks filled in with data repeatedly read out from the random memories to provide uninterrupted, coherent output signals. Fig. 4D, on the other hand, illustrates the reproduction of the original signals in duplicate Tape speed, where the frequency is twice as high as the original signal. In contrast to the previously described time axis stretching, in this case the applied time axis compression doubles the number of repetitions of the encoded pulses EPS compared to the repetition number of the decoded pulses DPS, so that the audio output signal according to FIG. 4E with respect to its frequency in comparison remains unchanged from the original signal. In the waveform of Figure 4E, one is missing Part of the waveform of the original signal because, as a result of the frequency setting, the The amount of data in the random memory has increased and excess data has been dropped have been.

Fig. 5 illustrates the details of the circuitry of the A / D converter 24 with the constant difference modulator.

This circuit consists of a signal input part 61, a comparator 62, a flip-flop 63, a local or local decoder 64 and an automatic Level setting circuit 65.

Other systems can also be used for analog / digital conversion Application of pulse code modulation (PCM) etc. can be used, although the device thereby complex and becomes expensive. In the illustrated embodiment the constant difference modulator is intended because it is simple and cost-saving is.

The audio input signal is made of one through the signal input part 61 Capacitor and a resistor and fed to the positive input terminal of the comparator 62 is applied, the minus input terminal of which is an analog-decoded Q output signal from the flip-flop 63 decreases, which is a sample corresponding to the encoded Contains pulse EPS. The audio input signal is thus in accordance with the previously of the clock of the encoded pulse EPS sampled or tapped input value compared and, depending on its size, converted into a digital signal ff of "1". The automatic level adjusting circuit 65 integrates the Q output of the flip-flop 63 with the time determined by resistor 66 and capacitor 67, and they feeds the result back to the audio input line via resistor 68, whereby the levels of the two input signals for the comparator 62 are automatically set will.

The outputs of the random memories 25 and 26, on the other hand, become as a series of continuous or continuous signals via the gate circuit 27 for Input terminal of the D / A converter 28 routed. The converter 28, which consists of a sample and hold flip-flop 281, a resistor 282 for integration and a capacitor 283 (cf. Fig. 6), is used to convert digital signals into analog signals. That of the timeline compander processing The signal that has been subjected to the digital / analog conversion finally ends up in the Low pass filter 29, of which frequencies above that through resistor 291 and the Capacitor 292 are not allowed to pass through a certain cut-off or blanking frequency, so that audio output signals are output with a reduced noise level.

The third embodiment of the invention shown in FIG. 7 comprises similar to the embodiment of Fig. 3, pulse oscillators 30A and 33A respectively the parts 30 and 33 and a control circuit 34A corresponding to the circuit 34. This device can operate in a manner similar to that illustrated in Figures 4A through 4K. In this embodiment, the random memories 25 and 26 are each made up of two random memory chips 251 and 252 or 261 and 262.

The random memories are initially set according to the level of the the signal applied to the read / write terminals into a write or read section divided. The two random storage groups or banks operate alternately Repetition of the writing and reading out complementary together, since the random memory 25 the read / write signal RW by or after division of the encoded pulse EPS from pulse generator 30A decreases while random memory 26 feeds the signal RW corresponding, but anti-phase read / write signal RW decreases. While thus, the random memory 25 is in the write-in mode, operates the random memory 26 after the readout mode and vice versa, so that the simultaneous continuous writing and reading of a number of signals is possible. The time axis compander processing according to the invention is based on a change the write and read speeds, this change being caused by the oscillators 30A and 33A, the control circuit 34A and the address counters 31 and 32 as follows is controlled: The control circuit 34A generates address pulses in which an encoded Pulse EPS from pulse oscillator 30A with varying pulse repetition frequency according to the setting of the compander ratio switching circuit 37 and a through the pulse oscillator 33A generated decoded pulse DPS with a fixed pulse repetition frequency occur alternately and in time with the read / write signal RW. These address pulses are transmitted to the address counters as address pulses APSA or APSB. the Address counters 31 and 32 provide designation addresses for the random memories 25th or 26 in such a way that the counter 31 or 32 counted size denotes an address in random memory and depending on the momentary Operating status Data written into or read from the specified address will. Also in this circuit is the repetition frequency of the address designation pulse when writing data is synchronized with the encoded pulse, while on the other hand the repetition frequency of the address pulse when reading out data with the decoded Pulse DPS is synchronous.

The signal compression or expansion thus takes place in the ratio of these two pulse repetition frequencies.

The output signals of the random memories 25 and 26 are then as a series of related or continuous signals via the gate circuit 27 to the input terminal of the D / A converter 28 conducted. The one from a flip-flop 281 for sample and hold purposes, a resistor 282 for integration and a capacitor 283 (see. Fig. 6) existing Converter 28 is used to convert digital signals into analog signals. The timeline compander processing subjected signals finally enter after the digital / analog conversion the low-pass filter 29, through which the resistor 291 and capacitor 292 certain blanking frequency lying frequencies are blocked, so that an output signal is emitted with a reduced interference level.

The device described above is used as a main component a random memory, i.e. a digital memory element which is saved by the basic system is controlled.

The device is thus circuit-wise around the memory simply constructed, that it is inexpensive to manufacture and has a high degree of reliability owns.

According to the invention, a novel mechanism is used in which two oscillators a free change in frequency of the write-in pulse allow, i.e. the setting of arbitrary or any compander ratios enable.

This circuit is therefore in comparison to the previous dividing system very simple, in which a write and read pulses by dividing basic clock pulses are formed.

The device according to FIG. 9, which is similar to the circuit according to FIG provided with a sound reproducing unit and a time axis compander unit which are separable from each other for the respective purpose. The output signal of the preamplifier 3 becomes the time axis compander circuit 4 via contact 40A of a changeover switch 40 and then via the contact 41A of a connection unit 41 entered. The output signal of this circuit 4 is sent to the loudspeaker 5 via the contact 41B of the connection unit 41 and the downstream contact 40B of the switch 40 fed. The switching circuit 6 supplies driver signals for control the control circuit 8 via the contact 41C of the connection unit 40 and the contact 40C of the switch 40. The contacts 40A to 40C of the switch 40 are with the Connection unit 41 can be connected. When the sound reproducing unit 42 and the compander unit 43 are put together, the changeover switches are switched to contacts b (Fig. 9), while the changeover switches are applied to contacts a when the units are separated from one another. The contact a of the switch part 40A is connected to the contact a of the via a line 1 Switch part 40B connected.

If the timeline compander function takes place with this arrangement, the connection unit 41 connects the sound reproduction unit in the manner shown 42 and the compander unit 43, the contacts or switch parts 40A to 40C of the switch 40 rest against the contact points b. The sound signal, the was reproduced from the magnetic tape 1 by the reproducing head 2 after amplification through the preamplifier 3 via the contacts or switch parts 40A and 41A the Compander circuit 4 fed and a time axis processing corresponding to Setting of the switching circuit 6 is subject. The sound signal treated in this way becomes Output from the loudspeaker 5 via the contacts or switch parts 41B and 40B. Of the Switching circuit 6 regulates the belt speed according to its setting, by sending the driver signal via contacts 41C and 40C to control the Drive 7 to drive control circuit 8 conducts.

When the connection unit 41 receives the sound reproduction unit 42 from the compander unit 43 separates, the contacts or

Switch parts 40A to 40C of the switch 40 in synchronism with of the connection unit 41 from the contact points b to the contact points a. Included the output signal of the preamplifier 3 from the contact point of the contact 40A is via the line 1 fed to the contact point a of the contact 40B and then via the Loudspeaker 5 fed out. The contact or switch part 40C also comes into contact the contact point a around, whereby the driver control circuit 8 internally short-circuited so that its output signal is fed to the drive or drive circuit 7 and the magnetic tape 1 at the normal sound recording / playback speed runs. If the two units mentioned are thus separated at the connection unit 41 the sound reproducing unit 42 only performs the normal recording / reproducing operations without timeline compression or expansion.

As in this device, the sound reproducing unit and the compander unit Can be optionally connected to one another or separated from one another by means of the connection unit , by connecting the two units, the time axis compander function performed while with separate units when no timeline processing required for normal recording and playback to take place. With the invention is thus a time axis Compander device created, which is versatile in terms of its mode of operation and low weight owns.

In the embodiment according to FIG. 9, the sound reproduction unit and the compander unit connected to one another by the connection unit, but can both units are also connected to the connection unit via connections, cables, etc. be.

Fig. 10 illustrates a reproduced sound speed changing device; in which the tape drive part 50 via the drive control circuit with the slide resistor or potentiometer 54 is connected.

The audio signals recorded on a magnetic tape 56 are transmitted through a playback head 58 converted into playback signals.

The playback head 58 is connected to a preamplifier 60, which the playback signal to one for performing the time axis compander operation required level is amplified and then to a compander ratio switching part 62 applies, which changes the compander ratio. The switching part 62 is with connected to a loudspeaker 66 through a time axis compander circuit 64, which those with a speed different from the speed of the original signal reproduced signals essentially without change or after analog / digital conversion by partially blanking or adding or multiplying compander processing subject.

In the illustrated embodiment, the switching part 62 is stepwise adjustable to different ratios, and if the speed is between Playback sound and original sound is 1 or close to 1, the signal from the preamplifier is used 60 immediately and oh> analog / digital conversion via a bypass circuit 68 from the loudspeaker removed. This is because it is beneficial a circuit should be used in which there is no possibility for deterioration the sound quality persists until the timeline compander processing is done got to.

When the potentiometer 54 and the switching part 62 in a certain Have been brought into positional relationship, they leave the drive control circuit 52 the Control tape drive part 50 so that the magnetic tape 56 at the same speed as in the original recording or driven at a different speed can be.

The modified audio signals sampled by the reproducing magnetic head 58 are amplified by the preamplifier 60 above the previously set Switching part 62 passed to the compander circuit 64, in which the timbre of the Sound signals are restored so that the sound signals are easy to understand Sound information can be emitted by the loudspeaker It must be pointed out that that the tape speed control part A, which at least the potentiometer 54 and the compander ratio switching part 62 of which at least one of the receptacles 'Playback mechanism containing unit is separated so that the latter through Remote control is controllable.

The potentiometer 54 and the conipander ratio switching part 62 are designed in such a way that, while maintaining the mentioned {mutual} Lateral relationship can be actuated and adjusted by means of a rotatable axis. These Setting or

Adjustment can be done depending on the chosen method for the timeline compander processing of tone signals are either continuous or gradual.

A pedal 72 is attached to the rotatable shaft 70 so that the Length ratio of the front to the rear section is about 2: 1. The pedal is against the force of springs 76 and 78 on a cradle 74 around axis 70 rotatable forwards and backwards. The springs 76 and 78 are at the front and rear, respectively The end of the pedal 72 is arranged between the latter and the pedal cradle 74. When the pedal 72 is tilted, the respective raised section separates from the upper end of its assigned spring, so that the foot operation can be done with little effort.

The belt speed control part A shown is designed in such a way that that when the pedal 74 is depressed in the forward or reverse direction, the playback speed is accelerated or slowed down. When the pressure exerted with the foot is released is done so that the pedal can return to its equilibrium state playback at normal speed.

Of course, the arrangement can be made so that when Depressing the rear part of the pedal increases the playback speed.

The pedal 72 can be in any position on the rotatable shaft 70 be attached.

In this embodiment of the invention can thus be seen the speed of the sound can be changed at will by simply pressing the pedal so that the operator has both hands to carry out for example is free from paperwork.

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Claims (10)

Time axis compression / expansion device for audio signals. Claims Time axis compression / expansion or compander device for audio signals, thereby characterized in that it comprises operator processing means, which at the playback of recorded audio signals with a different pitch (frequency pitch) than that at the time of recording, in one aspect of intelligibility the audio information impairing area, the audio frequency level of the recorded Step-by-step audio signals before they are fed into a time axis compander unit sets or varies and after performing a compander operation on the time axis the audio input signals output audio signals while in a tone frequency pitch range, in which tone or timbre changes without impairing intelligibility are possible, the audio frequency level of the audio input signal for delivery (to arrange) of audio output signals continuously. 2. Time axis compression / expansion or compander device for Sound signals, characterized in that they are an operator processing device which when the audio frequency pitch ratio between the recording audio signal and the sound signal to be fed to the device is 1 or close to 1, the Audio frequency level of the audio input signal for the delivery of audio output signals continuously and, if the ratio is greater than 1, the pitch frequency of the Sound input signal adjusts or varies (set) step by step and a compander processing performs on the time axis of the audio input signal to provide an audio output signal. 3. Apparatus according to claim 1 or 2, characterized by a Constant difference modulator for converting analog signals into digital signals, by memory for writing and reading out the digital signals with different Pulse repetition frequencies, through control circuits to control the pulse repetition frequencies, by a digital / analog or D / A converter for converting the digital signals from the memories in analog signals and by a level setting circuit, which the Automatically adjusts the input level by using the output signal of the constant difference modulator fed back to the input side. 4. Apparatus according to claim 1, characterized in that a low-pass filter intended for shaping the waveform of the analog signal supplied by the D / A converter is. 5. Device according to one of the preceding claims, characterized in that that they have an A / D converter for converting analog signals into digital signals, random memory for writing and reading out the digital signals with different Pulse repetition frequencies, control circuits for controlling the pulse repetition frequencies and a D / A converter for converting the digital signals from the random memories in analog signals and that the random memories in two rows or groups are carried out by repeating the writing and reading out of the digital signals in the time intervals determined by the control circuits in complementary relationship work. 6. Apparatus according to claim 3, characterized in that a low-pass filter intended for shaping the waveform of the analog signal supplied by the D / A converter is. 7. Device according to one of the preceding claims, characterized by an A / D converter for converting analog signals into digital signals Memory for writing and reading out the digital signals with different Pulse repetition frequencies, through control circuits for controlling a pulse generator, which is the output signal of a first pulse oscillator with a fixed frequency for the readout pulse for the memory and the output signal of a second pulse oscillator with variable Frequency makes the write pulse for the memory, and through a D / A converter for converting the digital signal from the memory into analog signals. 8. Apparatus according to claim 5, characterized in that a low-pass filter intended for shaping the waveform of the analog signal supplied by the D / A converter is. 9. Device according to one of the preceding claims, characterized in that that a sound reproduction unit with a sound pickup device for picking up sound signals from a sound recording medium, an amplifier for amplification the audio signals picked up and one Sound transducer for conversion the amplified audio signals into audible sound, a time axis compander unit for compressing or expanding the time axis of the audio signals in a predetermined compander ratio and a connection unit which has the sound reproduction unit and the compander unit to connect and separate from each other, and that the device is able to work in two modes as follows: If the connection unit has the The audio playback unit and the compander unit are connected to one another, becomes a time axis compander unit carried out; if the connection unit separates the sound reproduction unit and the compander unit, becomes a function similar to normal sound reproduction only by means of the sound reproduction unit carried out. 10. Sound playback speed controller for sound recording devices, thereby characterized in that a foot pedal having a time axis compander device for audio signals which is a pitch corresponding to the change in the audio signal playback speed of the recording device is able to convert to even when changing the playback speed It is far from easy to understand sound information, and one change operation part having a rotatable axis with which the frequency conversion accordingly the playback speed is variable that the controller in the form of the foot pedal connected to the rotatable axle and together with the compander unit from the recording device is arranged separately so that it can be operated remotely by means of the foot pedal, that the foot pedal is correspondingly in a rest position in the non-actuated state the normal sound signal playback speed and when stepping down on the one hand or the other side this speed increases or decreases, and that the controller puts the operating part in a defined relationship to the adjustment of the foot pedal able to bring down by trampling.