TL Audio A2 - Manual (Page 12)

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The Ebony A2 offers a wide range of ratios from 1:1.5 (gentle compression) through
to 1:30 (limiting). Limiting effectively clamps the input signal at the threshold level no
matter how much the signal is increased: this can be useful when trying to ensure that
the signal doesn’t exceed a certain level - for instance to prevent a digital recorder
distorting through overload.
Attack and Release.
The Attack time sets how quickly the compression is applied once the threshold has
been exceeded, and the Release time sets how quickly the compression is released
(and the signal returns to normal) once the signal drops back below the threshold. The
Ebony A2 Attack and Release controls each allow a choice of 2 switched positions
either ‘Slow’ or ‘Fast’.
The speed of the Attack and Release should in general be able to work with the tempo
of the signal. For example if the signal is a snare drum, by monitoring the gain
reduction it is possible to set the Release to allow the compression to fully recover (i.e.
the gain reduction needle will settle back to 0dB) before the next snare beat. This
prevents the second snare beat being reduced in level in comparison to the first. One
side-effect of having an incorrect release setting is distortion on low frequency signals,
which can particularly occur when using a fast release setting on bass heavy signals -
the compressor is forced in and out of compression during one cycle of the waveform,
and distortion results. The Ebony A2 has a built-in “Hold” facility which delays the
onset of release for approximately 10mS after the input signal falls below the
threshold. A slow release time should be used if distortion is still experienced.
Knee .
The Knee switch enables the Ebony A2 to be operated in two different modes - soft
Knee or hard Knee. Soft knee mode offers a gentle compression curve around the
threshold point, and is traditionally employed to yield a more subtle, musical type of
compression effect. The hard knee setting causes the full compression ratio to be
applied immediately the signal has passed the threshold point, so tends to produce
more pronounced and severe compression.
Gain Make Up.
While the subjective sound quality of the signal can be improved by compression, the
overall signal level will be reduced when gain reduction is taking place. The Gain
Make Up control is designed to boost the compressed signal by between 0 and 20dB,
in order to bring back the level to the same loudness as the uncompressed signal.
Without this control, comparing the original and compressed signals becomes
difficult, since there would be a level drop each time the compressor is switched in:
therefore it is normal to adjust the Gain Make Up control so that when the ‘compressor
on’ switch is activated, the audio signal remains constant in level.
Unlike the Output Level control, the Gain Make Up control is active only when the