[linux-dvb] 16-bit or 18-bit PCM output precision selected in firmware?

["Christoph-Sebastian Oesterheld" <coesterheld@snafu.de>]

Hello driver developers!

Wich setting use the firmware for the PCMSEL bit 1 of the
audio decoder control register (AUD_CTRL_REG) in the TMS320AV7110:

a) 0 for 16-bit PCM output or
b) 1 for 18-bit PCM output (default)?

This difference is very important for the 16-bit Audio-DAC of my Siemens
DVB-C (rev. 1.5),
the AKM AK4309B
(http://www.asahi-kasei.co.jp/akm/en/product/ak4309b/ak4309b.html).

The sound of the analog output of the Siemens DVB-C is not very good (like
an old 8-bit soundcard).
In contrast the sound of the SPDIF output is much better (tested with an
external connected DAC).

I have compared the specs of the DSP and the DAC:

In 18-bit PCM output mode, the audio decoder produce an 24-bit stream on the
PCM output.
The first 6 bits are zero, followed by the 18-bit PCM value.
The Audio-DAC ignores all preceding bits of an PCM bit stream with more than
16 bits.
As a result the Audio DAC processed the lower 16 bits of the 18-bit PCM
values
and this is could be the reason for the badly sound.

Over again, wich output precision use the firmware?
Can I force the 16-bit PCM output mode?
Perhaps my estimation is not correct an you have a better explanation?

greeting
Christoph Oesterheld



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