DE2049370A1 - Method and circuit arrangement for electronic evaluation, in particular, reverberation processes recorded on magnetic tape - Google Patents

Description

Method and circuit arrangement for electronic evaluation in particular Posting processes recorded on magnetic tape The invention relates to a method and circuit arrangements for electronic evaluation, in particular on magnetic tape recorded follow-up processes.

The evaluation of reverberation times is usually done in such a way that the reverberation process is recorded on magnetic tape and from the reverberation recording a tape loop is produced, which is played on a corresponding magnetic tape device will. The magnetic tape recorder in turn feeds a paper recorder via a third / octave filter, whose writing in the thirds or octaves is evaluated manually (graphically).

This method takes a relatively long time.

Therefore, electronic evaluation methods have been developed that avoid this deficiency (magazine for high frequency technology and electroacoustics, 1965, No. 3, pp. 86 to 91). Here, too, there is usually a detour via the belt loop selected, but after further processing of the playback signal during the decay process automatically from the time difference between the first time falling below two Level limit values exist, the reverberation time is determined and displayed.

The main disadvantage of this method is that decay processes, which show larger fluctuations in pee, are displayed with considerable errors. These errors can only be partially eliminated if more than two Limit values can be used for analysis. It should also be noted that sagging Nachhill curves, as z. B. occur in coupled rooms, not as such can be recognized and evaluated.

As before, what is described at the beginning is therefore still used in practice Evaluation method with paper strips is preferred because it covers the entire reverberation process to be used for identification and assessment, as this is a written Curve is present and can be assessed visually. Meanwhile others are electronic Evaluation devices become known (Acustica, Vol. 18, 1967, pp. 21 to 32), in which the neon signal via a logarithmic amplifier is an oscilloscope is supplied for display, the evaluation on its screen the reverberation time with calibrated masks (straight lines with different inclinations) will.

In the method of the invention, an oscilloscope is also used worked. However, the curves are not evaluated by measuring them on the screen, but in that the signal to be evaluated alternately or simultaneously, z. B. time-division multiplex, with an electronically generated, exponentially decaying comparison signal is written on the oscilloscope screen until registration is achieved is. In this way, a considerable gain in time is achieved in the evaluation, since a true-to-scale measurement is not required and the time scale can be changed without any expenditure of time can be.

In terms of circuitry, the method of the invention can be, for example realize in such a way that the comparison signal is obtained in an RC circuit becomes, the one in its hold time variable, the charging process of the capacitor of RC circuit controlling monostable multivibrator is connected upstream and its output leads to a changeover switch, the comparison signal and in one switch position in the other, the signal to be evaluated, preferably via a logarithmic one Amplifier and possibly a further amplifier to the horizontal pair of plates Oscillograph can get. The technical effort of such circuit is relatively low. Calibration errors in the logarithmic amplifier and in the oscilloscope cannot have any effect, as these components are identical for both measurements are.

It is useful to have a measuring potentiometer calibrated in seconds in the RC circuit to provide an immediate reading of the reverberation time after the both curves have been brought into congruence. Especially in the case where it is recommended to work with a tape recording or a tape loop to provide a start impulse on the tape that acts as a bistable multivibrator is supplied, which in turn controls the switch to the effect that the the desired alternating connection of the RC circuit and the signal source is established, so that after every second pulse passage the original sound position is restored is reached. If the signals are to be recorded at the same time, then comes the bistable multivibrator is no longer available. Instead, the monostable multivibrator is used connected directly to the output of the filter and the switch from an astable Multivibrator controlled, the switching frequency of which is above the highest to be evaluated Frequency of the reverberation signal.

The invention and its details are in the following with reference to a Block diagram explained in more detail.

The reverberation signal to be evaluated, which is here on a loop-shaped Magnetic tape 1 may be recorded, passes through a third / octave filter 2, a RMS rectifier 3 (input B) and a changeover switch 4 to the input of a logarithmic amplifier 5 to amplify the horizontal in an amplifier 6 Plate pair of an oscilloscope 11 to be supplied.

The signal is also fed to a filter 7 via input E2, in which a start pulse with the center frequency leading to the recorded reverberation signal fo is filtered out. With this start pulse, a bistable multivibrator is used 8 the switch 4 is controlled in such a way that the input of the logarithmic amplifier 5 alternately with the reverberation signal or a simulated reverberation signal which is obtained in an RC circuit 10.

Around the start time stamps of the reverberation signal and the simulated signal To be able to coordinate with each other, the RC circuit, which is calibrated in seconds Measuring potentiometer P2 contains a monostable multivibrator 9 connected upstream, the receives its impulses from the bistable multivibrator 8 ago. The hold time of this monostable multivibrator 9 can be changed with the help of a potentiometer P1, so that a temporal congruence comparison of the two decay processes on the oscilloscope can be done. During the discharge process, the decaying voltage of the Capacitor C via the switch 4 to the input of the logaritht mix amplifier 5 and the Oscilloscope 11 supplied, which its trigger pulses from the output of the filter 7 receives.

Another possible circuit is to use the bistable Multivibrator 8 to do without the monostable multivibrator 9 directly to the output of the filter 7 to connect and the switch 4 of an astable multivibrator to control, the switching frequency of which is higher than the highest frequency to be evaluated After-effects signal lies.

Claims.

Claims (5)

Claims 1. Process for electronic evaluation, especially on magnetic tape recorded follow-up processes using an oscilloscope, characterized in that, that the signal to be evaluated alternately or simultaneously, e.g. B. time-division multiplexed, with an electronically generated, exponentially decaying Comparison signal is written on the screen of the oscilloscope until a coincidence is achieved. 2. Circuit arrangement for performing the method according to claim 1, characterized in that the comparison signal is obtained in an RC circuit (10) which is a variable in its hold time, the charging process of the capacitor (C) the RC circuit controlling monostable Ndltivibrator (9) is connected upstream and the output of which leads to a changeover switch (4) which, in one switch position, controls the Comparison signal and in the other the signal to be evaluated, preferably via one logarithmic amplifier <5) and possibly a further amplifier (6) to the horizontal pair of plates of the oscilloscope 3. Circuit arrangement according to claim 2, characterized in that the RC circuit (10) contains a measuring potentiometer (P2) calibrated in seconds, which allows an immediate reading of the reverberation time after the two curves have been brought into congruence. 4. Circuit arrangement according to claim 2 or 3, characterized in that that the switch (4) is connected to a bistable multivibrator (8), the from one recorded in the presence of a magnetic tape record on the magnetic tape Start pulse (fO) controlled, the alternating connection of the RC circuit (10) and the signal source (1) to the logarithmic amplifier (5) concerned. 5. Circuit arrangement according to claims 2 to 4, characterized in that that, dispensing with the bistable multivibrator (8), the momostabile multivibrator (9) is connected directly to the output of the filter (7) and the switch (4) is controlled by an astable multivibrator, the switching frequency of which is above the the highest frequency of the reverberation signal to be evaluated.