Re: [LAD] FULL audio-signal path

On Sat, 2007-07-21 at 14:42 +0400, Andrew Gaydenko wrote: Adds noise. Soundcard must dither correctly (This sorts the linearity of the quantisation process), and means that the bit depth ONLY changes the noise floor, you can still detect signals down to below 1 LSB). Output is (In your case),24 bit samples packed into 32 bit words. Typically you actually get somewhere around 19 bits with the lowest few being swamped by thermal noise. All the Jack stuff converts to 32 bit floats, which provides for a 24 bit mantissa (Convenient that!). Jack converts back to soundcard native format (24 bit integer in 32 bit word IIRC for the HDSP), full sale is considered to be +-1.0 on the float side of the equation. For 16 bit cards, dither is optionally added to this conversion to linearise it. This is not considered necessary at 24 bit as the error is buried in the system noise for all practical systems anyway. Hdspmixer deals with DSP on the card, who knows what it does to the audio exactly? But it is probably done right. Alsa driver just passes along the DMA buffers from the card. Jack converts the integer sample values to floating point (Effectively lossless), and scales to +- 1.0 full scale (not saying that signals within the jack graph cannot exceed +-1.0, but that if they do at the output they will clip. Be very careful how you write float->int conversions (it is not trivial), and work in floating point as far as is possible, there is little reason (other then marketing) to move to doubles (IIR filters possibly excepted). When writing plugins, watch out for possible aliasing. With that card you do NOT need to be peaking at -1dbFS, you have plenty of dynamic range, so line up for your nominal zero level to be somewhere around -16 or so, you will loose far less takes to digital overs, and generally sweat less. Regards, Dan.