[alsa-devel] Output levels on SBLive! 5.1 on ALSA vs WIndows

[Takashi Iwai]

At Wed, 20 Jun 2007 17:12:39 +0800,
ChernYue Kwok wrote:
> 
> On Tuesday 19 June 2007 18:59:01 Takashi Iwai wrote:
> > At Mon, 18 Jun 2007 17:37:46 +0800,
> >
> > ChernYue Kwok wrote:
> > > Hello,
> > >
> > > I am using an SBLive! 5.1 sound card (emu10k1 chipset) with 6 channel
> > > output. Due to the nature of my work, I need to be able to play sound
> > > through all 6 channels at the same output level to an amplifier.
> > >
> > > Using Linux and the emu10k1 ALSA driver, I measured output voltage levels
> > > on an oscilloscope while playing a sine wave on all 6 channels, and I got
> > > three different output voltage amplitudes for the front, rear and
> > > center/subwoofer channels.
> > > Repeating the same test with the same card on WIndows using the Creative
> > > SBLive drivers from their website, I am able to get the same output
> > > voltage amplitude on all 6 channels.
> > > For both tests, all output levels in the relevant mixers were set to
> > > their maximum levels.
> > >
> > > I would like to know if this output normalizing 'feature' of the SBLive
> > > Windows driver can be found in the emu10k1 ALSA driver, or in any other
> > > ALSA driver. Failing that, is there any other solution to set output
> > > levels in the driver, or am I doomed to twiddle in alsamixer to get the
> > > output levels that I want?
> >
> > Did you check the dB level appearing in mixer?  The recent version of
> > ALSA shows dB level in alsamixer and amixer.  Note that the "Master"
> > and "PCM" controls are applied only for front channels.  So, set them
> > to 0dB and control the volume via Wave* digital mixers.
> >
> >
> > Takashi
> 
> Hi Takashi,
> 
> Thanks for your suggestions.
> Based on your advice on dB levels, I set the PCM and Master channels to 0dB 
> gain, and maxed the levels on the Center, LFE, and Surround channels.
> The Wave* channels were set to 0 since I was playing surround and not stereo 
> sound.
> 
> Playing the same 6-channel sine wave again, I was able to obtain the 
> following, more evenly matched, results:
> 
> Front channels: 0.64V peak to peak
> Rear channels: 0.68V peak to peak
> Center and subwoofer: 0.48V peak to peak
> 
> The front and rear channel output voltages were more evenly matched, but the 
> center/subwoofer channel shows a large difference from the other channels.
> For comparison, the results I obtained in Windows using the Creative SB Live 
> drivers are:
> 
> Front channels: 0.72V peak to peak
> Rear channels: 0.68V peak to peak
> Center and subwoofer: 0.64V peak to peak
> 
> Is there any way to increase output on the center and subwoofer channels in 
> ALSA?
> I already have the Center and LFE channels set to maximum gain in alsamixer, 
> so any suggestions to further boost the output are most certainly welcome. :)

Hm, this might have something to do with the signal routing in emu10k1
DSP code.  But I don't see obvious difference from other channels at a
quick glance of the code (emufx.c)...


Takashi