On Mon, 9 Jun 2008, stan wrote: > Grant wrote: >> I'm kind of an audiophile and I'd like to make sure there is no >> digital alteration being made to my music between the time it is >> decoded from FLAC and passed to the DAC via USB. We could argue about >> whether it makes a difference, but I'd just like to make sure there is >> a straight "pass-through" happening. >> >> The ALSA volume control and mute functions have no effect whatsoever >> on the volume of the sound, which is good. I used to use Rhythmbox >> which incorporated a software mixer for volume control. I now use mpd >> which does not use a software mixer, the volume control doesn't work, >> and that is good. It sounds a lot clearer. >> >> Can you guys tell me how else I should inspect my system's >> configuration for digital manipulation of my music? Would pulseaudio >> introduce this type of manipulation? >> >> - Grant >> >> > There are two additional reasons your sound will be altered between the > decode and the play. > 1. Conversion to your cards internal format e.g. from 16 bit signed > LE to 32 bit float That will at most give you digitization noise which at 16 bit is 96dB below full signal. Ie, it is much less than the tape hiss from a tape recorder for example. > 2. Rate conversion if it has a frame rate that isn't supported by your > card. e.g. The file > is encoded at 44100 frames/second, your card only supports 48000 > frames/second. > > The second one is the one you want to avoid. That requires resampling, > and depending on > the resampling algorithm used, can mangle your sound. I definitely agree that you want to avoid this . You might look at the tests I did with the SOX rate conversion routines. Note that if you are willing to take a long time, that rate conversion can be good. But it takes a lot of processing and time-- doing a good job in real time is hard. And linear interpolation, which is fast, is also terrible www.theory.physics.ubc.ca/soundcard/resample.html > > There really is no way to avoid the first one. Your card has to get the > sound in a format > it can understand, and if you have it in another format, there has to be > a translation. Unless the new format is terrible ( 8 bit audio for example) this should not matter. > > I'm not sure about puleaudio, but I think, like jack, it opens the card > at a fixed rate, and > everything is converted to that rate. > ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
