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Audio Signal Processing

IP.com Disclosure Number: IPCOM000073447D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Maling, GC: AUTHOR

Abstract

In many situations when it is desired to measure the amplitude and/or time history of a nonstationary acoustical noise, the dynamic range of the measuring system is not sufficient, and must be changed during the acquisition of data. The changing of system gain has not been a major problem in the past because the instrumentation has generally been manually operated, and the operator can adjust gain to keep the signal within the desired range. One automatic gain amplifier that is available has the property that the amplifier gain is a discrete function of the full-wave-rectified-average signal going through it. However, experiments using the available auto-gain amplifier have shown that the system can become overloaded (clipped) for signals of high crest factor (peak-to-rms ratio).

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Audio Signal Processing

In many situations when it is desired to measure the amplitude and/or time history of a nonstationary acoustical noise, the dynamic range of the measuring system is not sufficient, and must be changed during the acquisition of data. The changing of system gain has not been a major problem in the past because the instrumentation has generally been manually operated, and the operator can adjust gain to keep the signal within the desired range.

One automatic gain amplifier that is available has the property that the amplifier gain is a discrete function of the full-wave-rectified-average signal going through it. However, experiments using the available auto-gain amplifier have shown that the system can become overloaded (clipped) for signals of high crest factor (peak-to-rms ratio). Thus, adjustment of the system gain on the basis of the full-wave-rectified-average will cause the peaks of the signal to clip and an accurate measurement of the rms value of the signal is not possible.

In this system, the peak (or quasi-peak) is used to adjust the system gain, and a signal related to this peak is passed through the auto-gain amplifier together with the actual signal. Separation takes place in the notch filter following the auto-gain amplifier.

The diagram illustrates a system in which the signal input A and a peak chopped input B (filtered) are mixed in amplifier 10. The auto-gain amplifier 12 then passes the sum of these two signals. Because the...