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[hfsig] Performance of 24/192 soundcards? USB Soundcards

Thomas Sailer t.sailer at alumni.ethz.ch
Mon Sep 20 19:35:29 UTC 2004


On Mon, 2004-09-20 at 18:34, Robert McGwier wrote:
> PLEASE check again.  That is the USB sound card that I have
> that does 24 bits.
> 
> I would love for you to tell me it worked.  I never could get
> it to work.

$ uname -a
Linux gamecube.scs.ch 2.6.8-1.521 #1 Mon Aug 16 09:01:18 EDT 2004 i686 athlon i386 GNU/Linux
$ cat /etc/fedora-release
Fedora Core release 2 (Tettnang)

Stock Fedora Core 2 setup, with the latest errata kernel.

$ cat /proc/asound/cards
0 [rev50          ]: VIA686A - VIA 82C686A/B rev50
                     VIA 82C686A/B rev50 at 0x1000, irq 5
1 [NX             ]: USB-Audio - SB Audigy 2 NX
                     Creative Technology Ltd SB Audigy 2 NX at usb-0000:00:07.2-1, full speed

I've just tested my own digital radio application, that sets the card up
in a somewhat strange configuration:
- Recording with 96kSamples/s, 24bit
- Playback at 48kSamples/s, 16bit

I'm using the native ALSA API.

Hardware PCM card 1 'SB Audigy 2 NX' device 0 subdevice 0

Its setup is:
stream       : CAPTURE
access       : RW_INTERLEAVED
format       : S24_3LE
subformat    : STD
channels     : 2
rate         : 96000
exact rate   : 96000 (96000/1)
msbits       : 24
buffer_size  : 10922
period_size  : 5461
period_time  : 56885
tick_time    : 1000
tstamp_mode  : MMAP
period_step  : 1
sleep_min    : 0
avail_min    : 5461
xfer_align   : 1
start_threshold  : 2147483647
stop_threshold   : 10922
silence_threshold: 0
silence_size : 0
boundary     : 1431568384
Hardware PCM card 1 'SB Audigy 2 NX' device 0 subdevice 0

Its setup is:
stream       : PLAYBACK
access       : RW_INTERLEAVED
format       : S16_LE
subformat    : STD
channels     : 2
rate         : 48000
exact rate   : 48000 (48000/1)
msbits       : 16
buffer_size  : 16384
period_size  : 4800
period_time  : 100000
tick_time    : 1000
tstamp_mode  : MMAP
period_step  : 1
sleep_min    : 0
avail_min    : 4800
xfer_align   : 1
start_threshold  : 2147483647
stop_threshold   : 16384
silence_threshold: 0
silence_size : 0
boundary     : 1073741824

Works as expected.

One advice though: use the ALSA driver using the native API. The OSS
emulation tries to do some sampling rate conversion, which is good
enough for audio (now some high end audio types will want to kill
me...), but it apparently introduces sample time jitter.

Tom






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