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

[Ralph Metzler <rjkm@convergence.de>]

Christoph-Sebastian Oesterheld writes:
 > 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?
 > 


As far as I can see it audio is set to use 16-bit PCM during the 
initialization in the firmware. Since this is done thrugh an RTSL call
I don't know if they set the control register bits in the way you
described but I would guess so.


Ralph


-- 
Info:
To unsubscribe send a mail to listar@linuxtv.org with "unsubscribe linux-dvb" as subject.