Specifications
Setting Up The Processing
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Without hold With hold
Unless you have a specific reason to turn it off we recommend a setting of around -32dB but this may need to be
increased or decreased depending on drive levels into the limiter and how much effect you want the hold control
to have on the audio. If set too low you will rob yourself off some loudness, if set too high you will lose some of
the benefits of the mechanism by letting the limiter release too far before gating.
Delay
The delay control sets the amount of time the processor will hold the gain reduction for before releasing at the
peak decay rate. Careful setting of this control allows us to speed up the peak decay time without introducing the
audible effects of faster decay times. Setting this control to 1 is a negligible amount of delay before decay which
is equivalent to the delay being switched out of circuit. As you go up through the bands you will need lower delay
numbers to avoid causing audible problems being introduced by the delay circuit. We have found that bands 3
and 4 work well with settings of 2-4, band 2 settings for 3-6 and band 1 settings of 5-8. Setting the control to 10
introduces almost half a second of delay before decay so make sure you don’t use the higher settings of this
control on anything other than band 1.
If you are unsure about this control we suggest you set it to 1 to turn it OFF.
The mixer
The post limiters mixer in the DSPXtreme is not strictly a mixer but a band output level control where small EQ
changes can be made. It has been called the mixer as most other processors have a mixer at this position and
our VIRTUAL mixer does the same job. Bands 1 and 2 do mix together at this point , so do 3 and 4 and also 5
and 6 so I suppose you could call it a half-mixer. The six bands have become three.
Be careful when making large EQ changes at this stage because there is no peak control prior to the clipping
system. It is easy to overload the clipping stages by setting these controls all to large positive values.
The control range for each band of +/- 3dB is purposely restricted for the above reasons.
The multi-band clipper
While the outputs of the multi-band limiters are peak limited they suffer from overshoot. The audio waveform
can pass through before the limiter has time to 'attack' the signal. This is not a design flaw in the limiter but a
required response. If you remember from our earlier discussions about audio processing you will recall that the
processing can sound more natural and dynamic if a limiter lets sharp transients through rather than clamping
down the whole audio signal whenever a transient occurs. These small transients can audibly dominate the limit-
ing if the attack time of the limiter is too fast. It is much better to let these small transients through and deal with
them in the next stage of processing.
The multi-band clipper that follows the multi-band limiters is designed to deal with these limiter overshoots and
clip them to a pre-defined level. You may also recall from our earlier discussions on processing that clipping tran-
sients and overshoots is pretty much inaudible if done in moderation. The combination of the multi-band limiters
and multi-band clippers provides us with the perfect answer. The limiters control the peaks of the audio but suffer
from overshoot, the clippers then provide us with a true defined peak ceiling. Because the limiters precede the
clippers we won't suffer from clipper overload induced distortion because the clippers are being fed with audio
that has a pretty constant peak level. We also gain the advantage of more dynamic natural sound from the limit-
ers because we are not worrying about overshoot and can set the attack times of the limiters higher than what
would have been possible without the multi-band clippers.
Radio stations have a desire to be competitively loud and clipping is the easiest and most effective way in gain-
ing loudness in a processor. While clipping is effective there is only so far you can push a clipper before notice-
able distortion occurs. We can push this boundary of distortion back further by filtering out some of the distortion
post clipper. By filtering after the clippers we are able to significantly reduce audible distortion.
The DSPXtreme multi-band clipper has three clippers and three post clipper filters. Bands 1 and 2 sum to serve