Date 21.6.2011 13:55, Pierre Habraken wrote: > On 06/20/2011 10:06 PM, alsa-user-request@xxxxxxxxxxxxxxxxxxxxx wrote: >> >> Date: Mon, 20 Jun 2011 22:34:46 +0400 >> From: Vladimir Mosgalin<mosgalin@xxxxxxxxxxxxxxx> >> Subject: Re: plughw versus hw >> To: alsa-user@xxxxxxxxxxxxxxxxxxxxx >> Message-ID:<20110620183446.GA14919@xxxxxxxxxxxxxxx> >> Content-Type: text/plain; charset=us-ascii >> >> Hi Pierre Habraken! >> >> On 2011.06.20 at 19:32:28 +0200, Pierre Habraken wrote next: >> >>> I can imagine that this is a FAQ, but I could not find a clear answer : >>> which precise difference(s) distinguish(es) plughw and hw from each other ? >>> Does plughw apply sound processing that hw does not ? >> >> plughw *might* apply simple sound processing if needed, mostly channels >> conversion and rate conversion if required. It doesn't have to apply >> processing. >> hw doesn't support such processing only works when operating strictly in >> mode that audio card support. >> >> If you have device that supports only 2 channel, 16 bit 48000 mode then >> "hw" device won't be able to playback 2/16/44100 stream, or mono stream >> for example; you'll get an error when you try. But plughw will accept >> such streams and do the conversion. However, if you use plughw and >> output 2/16/48000 stream then no conversion is needed and most likely >> plughw won't be doing any processing. >> >> Note that using both hw and plughw can lead to specific problems, so >> it's best to use "default" device unless you have very specific >> requirements. > > Hello Vladimir, > > Thank you for your reply. > > I just bought an Asus Xonar DX sound card, for sending 24bits/96KHz > stereo flac files to an external DAC. > I am using Alsa 1.0.21 on a PC running Ubuntu 10.04 with Linux kernel > 2.6.32-32. > Running aplay, I can't use hw for reading 24/96 files: > > $ aplay -D hw:0,1 Prelude.wav > Playing WAVE 'Prelude.wav' : Signed 24 bit Little Endian in 3bytes, Rate > 96000 Hz, Stereo > aplay: set_params:990: Sample format non available > Available formats: > - S16_LE > - S32_LE > $ > > Adding the switch -f S32_LE does not help: > > $ aplay -D hw:0,1 -f S32_LE Prelude.wav > Warning: format is changed to S24_3LE > Playing WAVE 'Prelude.wav' : Signed 24 bit Little Endian in 3bytes, Rate > 96000 Hz, Stereo > aplay: set_params:990: Sample format non available > Available formats: > - S16_LE > - S32_LE > $ > > If I use plughw instead of hw, it works fine: > > $ aplay -D plughw:0,1 Prelude.wav > Playing WAVE 'Prelude.wav' : Signed 24 bit Little Endian in 3bytes, Rate > 96000 Hz, Stereo > ^CAborted by signal Interrupt... > $ > > Does it mean that the 24bits stream has to be converted to 16bits before > being sent to the device and then to the DAC ? No, use 'aplay -v' to see all plugins used by plughw. Your hw supports 24-bit samples encoded in the 32-bit words. So alsa-lib does 3-byte to 4-byte conversion of 24-bit samples - audio bits are not lost. Jaroslav -- Jaroslav Kysela <perex@xxxxxxxx> Linux Kernel Sound Maintainer ALSA Project; Red Hat, Inc. ------------------------------------------------------------------------------ EditLive Enterprise is the world's most technically advanced content authoring tool. Experience the power of Track Changes, Inline Image Editing and ensure content is compliant with Accessibility Checking. http://p.sf.net/sfu/ephox-dev2dev _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
