Telex ISP-100 manual Metering, Bypass, Overshoot, Computation of Average Level, Sidechaining

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input signal was going to be, then the Crest Factor Sensitivity control would ideally be set to:

1

Crest Factor of Input Signal

Since this quantity is not generally known, it is best to experiment until satisfactory results are obtained.

Metering

The compressor meter shows the attenuation applied to the signal passing through the compressor at any given moment in time. When the signal is being compressed the meter indicates negative values (gain less than 1.0). When the signal is not being compressed the meter indicates 0 dB (gain of 1.0). Meter values are raw, no averaging or ballistics are applied.

Notes on Operation of the Compressor

Bypass

Bypassing a compressor causes the signal to pass through unaltered.

Overshoot

The compressor algorithm used in the ISP-100 allows for a small amount of overshoot on transients, regardless of the settings of the Detection Window and Crest Factor Sensitivity controls. The amount of overshoot is somewhat dependent upon the setting of the Threshold control; the lower the threshold the greater the overshoot. This represents normal operation for the compressor.

Computation of Average Level

There are two common methods of computing average signal level; one is based upon RMS (Root Mean Square) calculations, and the other is based upon Absolute Value calculations. Each of these methods produces a slightly different value for signal level, and the difference depends upon the characteristics of the signal itself. The ISP-100 compressor uses Absolute Value for its computation of signal level, so the level reported by the compressor may differ slightly from the RMS value expected for a given signal.

Crest Factor Sensitivity and Sinewaves

The peak level of a pure sinewave tone is 1.414 times its average level. The ISP-100 compressor will therefore apply approximately 3 dB more compression to a pure sinewave signal when the Crest Factor Sensitivity is set to 1.00 (peak- responding) than when it is set to 0.00 (average-responding). This represents normal operation for the compressor.

Sidechaining

When the sidechain input to an ISP-100 compressor is selected to be a channel other than its input, the compressor controls must still be set. The sidechain selects only the channel’s data,

10 July 1998