CLAS/NR - Compressive Loudness Audio Shaping with Noise Reduction

The CLAS plugin has been a huge smash with recording engineers and artists alike. But one of the problems with this kind of processing, when used at high relative treble enhancment levels as an exciter, is an increase in high-frequency noise and hiss. This is particularly troublesome for live sessions and old recordings.


To overcome this problem when recording, we have implemented a variant of CLAS that incorporates a sliding-filter Noise Reduction unit ahead of the CLAS processing. Analog implementations of sliding-filter noise reduction have been used in the past to implement Dolby-B and Dolby-C noise reduction encoding. We are doing it here, for the first time, in digital form.

In practice, one simply adjusts the Threshold for noise reduction until, under ambient noise levels, one sees the Noise Reduction meter fully closed down. The two red-bars on the left extend all the way to the bottom. At thresholds just below that point, you will see the noise-reduction bars dancing up and down.

If Threshold is set too far below your actual noise levels, then of course the noise-reduction bars retract all the way up, indicating that it thinks signal is present. The same happens with any noise gate technology.

Conversely, with this kind of noise reduction scheme, setting the threshold too far above the actual noise level will produce "noise modulation" on actual signals - a kind of stuttering sound. That typically happens when your threshold is 20 dB or more above the actual noise level, and it occurs because the sliding-filters are biting into the top of your sound spectrum in an effort to eat that much "noise".

But when adjusted properly, and this is very easy to do with our Noise Reduction bar graph, the sliding-filter noise reduction technique works very well indeed. With Noise Reduction ahead of CLAS processing, you can safely boost the highs without fear of undue noise degradation. As soon as the signal falls away, the sliding-filter slams shut, keeping noise at bay.

CLAS-NR uses upsampling ahead of the filtering for sample rates below 80 kHz, using a slightly different technique than our PLParEQ, but for the same kind of quality improvements. Filtered results are downsampled again to your system sample rate. The upsampling used is much lighter weight than PLParEQ requiring much lower CPU loading. (Note: the free CLAS plugin does not perform this high SR filtering.)

CLAS-NR uses 64-bit computation throughout, and it is 64-bit ready for Sonar 5. For 24/32 bit systems, the 64-bit results are dithered back to your host wordsize using our sophisticated Gaussian PDF dither.

CLAS-NR performs equally well in stereo or on mono tracks, using autosensing of the host connections. (Some hosts do not advertise Mono inserts properly).

CLAS-NR can accommodate all sample rates.


more info available at:

http://refinedaudiometrics.com