adt-audio
ToolMod
®
Pro-Audio Module System
TM215b - Stereo Mastering Peak-Limiter
6
➔
Set the dynamic release to the highest value that causes no pumping!
Like the
static release, the dynamic release increases the release time - in this case depending
on the density of the signal - that may cause pumping. Usually you can reduce the sta-
tic release time when you use dynamic release. Try both until you get the best possi-
ble compromise for the lf distortion without pumping.
In rare cases it might be necessary to reduce the gain reduction, which will reduce both
problems even if the reduction is only 0.5 dB.
Please note:
The more you open the dynamic release pot, the longer is the release time of the long
time integration circuitry that measures the density and the longer it takes before a chan-
ged setting is in effect. Wait a couple of seconds before you judge a new setting.
Attack Time
The Attack setting determines how fast the limiter reacts when the level exceeds
threshold. In opposite to an analog tape recorder that causes no audible distortion
with short peaks, a/d converters are extremely sensitive to overloads, even from a ve-
ry short peak. To catch such peaks, the attack time should be as short as even possi-
ble. However, with short attack times the attack distortion problem appears. With short
attack times and low frequencies, the control signal for the regulator follows the mo-
mentary value of the wave form of the audio signal. As soon as the momentary value
exceeds threshold, regulation starts right away. With the TM215b the delay between
crossing threshold and regulation is less than 8 µs. The regulation disrupts the wave-
form by putting a hard edge into the signal, which will result in additional harmonics.
This effect takes place only for the half wave that triggers regulation. If a short dis-
tortion that might appear as some kind of click noise or scratching is audible depends
on the frequency, the spectrum and the gain reduction. Most critical are low frequen-
cy signals with a low portion of harmonics. Attack distortion is a physical problem that
depends on the combination of attack time and signal structure and not on a particu-
lar principle of regulation, components, and the like. With an attack time of approx.
1 ms, these effects disappear; however, with such a long attack time short peaks will
pass thru the limiter without causing regulation.
