On Wed, 17.02.10 11:30, Raymond Yau (superquad.vortex2@gmail.com) wrote:
2010/2/16 Lennart Poettering mznyfn@0pointer.de
On Tue, 16.02.10 09:08, Clemens Ladisch (clemens@ladisch.de) wrote:
Lennart Poettering wrote:
Getting back to the invalid dB data from the USB cards: the question is whether the USB descriptor data is badly parsed, and the dB mismatch hence systematic for USB cards,
USB descriptors use units of 1/256th dB, while ALSA uses 1/100th dB. When the level is computed from the minimum plus a multiple of the step size, rounding errors add up considerately.
ALSA 1.0.21 (kernel 2.6.32) added a different TLV type that reports the range with the min/max values to minimize those rounding errors.
I am really sure that the discrepancy I measure with the Aureon is way beyond rounding errors.
Lennart
if the program use a format FLOAT_LE which is not supported by the hardware and need to use plughw , you have already added error ( resampling and format conversion ) to the result
That numeric noise is neglible in contrast to the big (20dB or so?) discrepancy I am seeing here.
Lennart