Setting Up The Processing
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liseconds, reducing loudness and creating audible pumping effects.
The solution is multiple time constants where one set of time constants can be set to handle the fast peaks and
another to handle the average level of limiting. Fast transients will release in a faster less noticeable way and
won't punch holes in the sound in a way that single time constant limiters can. The secondary slower time con-
stant circuit will not have much effect on the audio waveform when hit with a transient because the higher attack
time, generally in the hundreds of milliseconds will not allow a build up of energy. In the case of a sustained
envelope of audio above the threshold the multiple time constant will attack as normal with the peak time con-
stant but the sustained energy will also charge the secondary slower circuit. When the audio energy falls away
and the circuit goes into release the peak decay will dominate until it reaches a point where it hands over to the
slower secondary time constant for a slower rate of decay. The illustrations show this to good effect, where tran-
sients have a fast release but multiple or sustained transients build up energy in the secondary circuit which acts
as a platform for the peak to release to. The secondary circuit's platform can be thought of as the average level
of limiting. Having this fast peak responding circuit ride on top of the average circuit creates many advantages,
limiter transparency, less chance of pumping and greater loudness. By setting the time constants appropriately
we can have the multiple time constant based detectors work as peak handling, average handling or the opti-
mum setting of a balance of the two.
The peak attack time should be set to the desired attack time required from that limiter. The range is 1-10 which
corresponds to 1 to 200mS on an exponential scale. The peak decay time should be set to the desired peak
decay time required for transients. The range is 1-10 which corresponds to a decay time of 10 to 1000mS.
The average attack time is perhaps the most important control in the dual time constant detector as it sets the
balance between peak and average energy in the detector. With smaller numbers more energy is transferred
into the average circuit and a higher platform level is created so more time will be spent releasing at the slower
average rate. Higher numbers offer slower attack times for the averaging part of the detector and this has the
effect of lowering the average platform level and allowing the peak part of the circuit to dominate with its faster
release times.
The average decay time can usually be viewed as the nominal release time of the detector, similar to a standard
single time constant limiters release time.
To recap, the peak attack time and average decay time play the same sort of role as that of a standard con-
ventional single time constant based limiter. The peak decay time sets the decay time for fast usually inaudible
Peak time constants dominating control due to
a very high setting of average attack
Peak time constants dominating to a lesser
degree due to high setting of average attack
Peak time constants dominating to a much
lesser degree due to a lower setting of average
attack
Limiter control signals response to tone bursts
Peak time constants dominating control due to
a very high setting of average attack
Peak time constants dominating to a lesser
degree due to a high setting of average attack
Peak time constants dominating to a much
lesser degree due to a lower setting of average
attack
Limiter control signals response to program material
