Bugzilla – Bug 4884
enhancement: realtime audio compression
Last modified: 2011-11-06 23:24:21 UTC
When listening to audio late at night, it would be very cool to have an audio level compression 'feature'. Not file compression, but level compression like a Universal Audio LA2a would do. The DAW software for recording have many flavors of audio compressors and limiters. Something like a FMR Audio RNC would be enough. I think it would be best to be in the hardware firmware, but clearly a server side plugin could work, altho recompressing the audio to Flac would be a challenge for slow servers.
Seems like a reasonable idea, but we'd need more details on how it would work, what kind of compression/limiting would be involved, etc...
Well, at the simplest, you would have a compressor with knee and level. Feed the audio in, and have the compressor do its DSP thing, and output the stream. Essentially a simple filter. Of course, you would need parameters to the compressor for whatever parameters it has. A fair number of them have at least three: "knee (soft or hard)", amount (how many dB to compress), and "makeup gain" or how much to raise the resulting level. Most real compressors do not raise the soft sounds, they lower the loud ones. You feed it a 96 dB signal, and get out a 60 dB signal. Then you raise the gain on all of the signal by 36dB to recover the lost gain. This makes old loud sounds stay loud, and old soft sounds be 36 dB louder. This raises the question of what compression plugin to use. Do you want just a compressor? or compressor/limiter? How many controls, while a LA2a has only two, other have three or four controls. And then there are multi-band compressors. They can have many bands, lets talk about three: 1) bass (20 to 200 hz) 2) mid (200 hz to 1500) 3) high (1500 up) with separate gain/limit values for each. Then you can have movable bands, say 20 to 300 hz instead of my 20-200.
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