Sonnox Oxford SuprEsser - Manual (Page 16)

3.3 AdvancedOperation 3 OPERATION
into the compressed signal. This can be used to create that unique sound in which a fully
compressed signal (with no dynamic headroom) has some punch added back into it.
In this mode, the LISTEN section has no effect on the signal because the output of the
compressor is already a complete wide-spectrum signal.
3.3.2 AutomaticLevelTracking
Auto Level Tracking mode is enabled by selecting the LEVEL TRACKING/AUTO IN button.
This is ON by default.
The purpose of this mode is to automatically adjust the threshold level to follow the
general signal level of the wide-band input. This means that if some vocals wander from
loud to quiet, the same amount of relative gain reduction is applied when a transient peak
occurs above the general level.
Generally speaking, once you have isolated as narrowly as possible a troublesome sound
in the frequency spectrum, you will see the red peak-hold marker, inside the bandpass
filter on the graphic display, indicating the peak level of the troublesome sound. Now
enable Auto Track mode, and bring the THRESHOLD level down until its corresponding
line on the graph is below the red line. You will then see the gain reduction meter
(ATTENUATION) starting to show gain reduction.
If the general signal level of the material changes, the threshold will now follow that level,
so that the gain reduction meter should continue to indicate the same amount of
reduction of the peaks.
The algorithm to track the general signal level is not as simple as it appears. First, one of
the most important characteristics of speech is its staccato nature, and the frequent
pauses or silence. If the threshold truly followed the signal level, each time there was a
pause broken by a word starting with a consonant, the threshold would have fallen too
low, and the consonant would be over gain-reduced before the threshold recovered its
normal level.
To get around this challenge, the algorithm implements a working range of 24dB, and any
sample value outside this window is not included in the calculation of the general signal
level. If you were to intermittently mute the input signal, you will see that the threshold
effectively just stays where it was when there was an active signal, and continues tracking
again when the active signal is restored. Yet if you slowly fade out the input signal level,
the threshold will follow, only giving up after 36dB of gain reduction.
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