Decimate the audio path to improve NR functions #4
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Decimate the audio path for processing down from the raw 44kHz to 11kHz. The main goal here is not to reduce the processing overheads (although it does drop a 'full' SSB NR compute from 20% down to 7%), but is to allow the noise reductions that use 'bins' to focus those bins on the audio spectrom (0-5.5kHz), rather than spread them across the full CD quality bandwidth (0-24kHz). We *could* have bumped the number of bins in the NR systems (from 128 iirc) to get the same effect maybe, but then that would have cost us more CPU time for the same gain?? The change seems to help. Now we need to see if it helps when combined with the FIR bandpass normalisation code... Fixes: #2 Signed-off-by: Graham Whaley <[email protected]>
Update the README to note we have moved to decimating the audio path. Also bump the version, as this is quite a large change. Add a version history table to help track changes. Signed-off-by: Graham Whaley <[email protected]>
Fix the link to the feature-list section. Fix a typo. Signed-off-by: Graham Whaley <[email protected]>
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Decimate the audio path x4 (from 44kHz down to 11kHz).
The main benefit is it allows some of the processing, like the noise reduction methods, that are based on 'slots' to have finer granularity when working on the audio spectrum. Previously they would process ~0-22kHz. Now they process ~0-5.5kHz - so, 4x the granularity of filter frequency bins.
An added benefit is the CPU overhead is also reduced. With Spectral, glitch and notch we were at ~20%. With decimation we are now at ~7%.