Refined Audiometrics Laboratory

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CLAS - Compressive Loudness Audio Shaping

CLAS (Compressive Loudness Audio Shaping) is a tool that provides both progressive phase compensation for bass frequencies, and psychoacoustic bass and/or treble enhancement. We use CLAS most often when listening to track edits on the master channel, purely for our pleasure.

(click image for full-size preview)

The effect is similar to BBE treatment, but without being "in your face!". Psychoacoustic compression is similar to many classic compression curves, producing the most boost at low sound levels, and progressively tapering off to no-boost at extreme loud levels. This is more pleasing to listen to than typical linear compression, and accounts for the appeal of many classic analog compressors. The effect, in CLAS, is much like dynamic Loudness Contouring.

CLAS works best on Stereo channels, but it is also capable of running on Mono tracks. The left and right channel compressors are tied together in order to retain stereo field balance.

The progressive bass group delay acts almost independently of the bass and treble enhancement. Bass and treble enhancement are separately applied. The enhancement levels are nonlinear functions of the actual dB boost provided internally, so we map them to the faders for you so that you get the boost you ask for.

Classic "Psychoacoustic" Compression

Progressive Bass Group Delay - shown to be a weak function of bass boost,
for boosts of 0 dB (green), 5 dB (orange), and 10 dB (red).

Bass and Treble Enhancement

While shown together in the above graph, the bass and treble boosts are really applied separately and need not be the same amount. These boosts are the maximum applied, for low level audio signals. The compression threshold is fixed at -30 dBFS, and so even at maximum boosts of +12 dB, music never approaches the clipping level as a result of these boosts. Attack time is 25 ms and release is 250 ms, with a 15 ms hold, sufficient to avoid pumping even at 30 Hz.

What is it? CLAS is simply the mix of your audio sent in parallel through a 2-pole Lowpass filter tuned to 725 Hz, and a 2-pole Highpass filter tuned also to 725 Hz. The Q of each filter is 0.2. Then half the original signal is subtracted from the sum of these filter outputs. Boost is applied to the two filters, and this boost is a function of the psychoacoustic compression curve shown above. Simple!

Send us a note for your copy of this Windows/VST plugin. Enjoy some quality listening!