> Thank you for all this information!
You're welcome, I had that much difficulties in finding these mapping
that I'm happy to see it can be usefull for other devices ;-)
> I'll need some time to check what is needed for the Fast Track Pro.
In fact it's not that tricky: just install a usb sniffer under windows,
then play with the control panel and check the SELECT_INTERFACE
messages for Interface/AlternateSetting. With the audiophile USB, it
only changes:
* if you change the bit depth
* if you change the sampling rate
* if you enable/disable the SPDIF input
> I think there is a big chance that many things are handled the same
> way like Audiophile. At least the number of Channels and also the
> mapping of digital an analog interfaces are the same. I tried to
> connect directly to the 24-Bit mode after startup of the USB device
> and I had the same "wrong" signal on both channels. This makes me
> positve to believe that the byte alignement (like you described) gets
> mixed up after mode switching.
Yes that sounds exactly the same...
> The distortion I head on both channels could have something to do
> with endianess. Instead of a sine wave I had a 3rd Harmonic at level
> of about -55dB (in the range of one byte) and the noise level was
> about -80dB (the range of the second byte).
The relevant section in usbaudio.c is the "is_big_endian_format" function.
Maybe just testing by adding your usb_id in this function will correct
endianness ?
See:
2297 /* 2298 * check if the device uses big-endian samples 2299 */ 2300
static int is_big_endian_format(struct snd_usb_audio *chip, struct
audioformat *fp) 2301 { 2302 switch (chip->usb_id) { 2303 case
USB_ID(0x0763, 0x2001): /* M-Audio Quattro: captured data only */ 2304
if (fp->endpoint & USB_DIR_IN) 2305 return 1; 2306 break; 2307 case
USB_ID(0x0763, 0x2003): /* M-Audio Audiophile USB */ 2308 return 1;
2309 } 2310 return 0; 2311 }
Regards,
Thibault
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