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 ? Pierre ------------------------------------------------------------------------------ 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
