[pulseaudio-discuss] Weak bass in stereo mode – possibility of virtual 2.1 sound profiles

Alexander E. Patrakov patrakov at gmail.com
Sun Nov 25 19:17:53 UTC 2018

On 11/16/18 11:13 AM, Tanu Kaskinen wrote:
> On Thu, 2018-11-15 at 23:50 +0500, Alexander E. Patrakov wrote:
>> Alexander E. Patrakov <patrakov at gmail.com>:
>>> Tanu Kaskinen <tanuk at iki.fi>:
>>>> On Sat, 2018-10-13 at 22:29 +0500, Alexander E. Patrakov wrote:
>>>>> Note that I am unhappy with it, because it fixes only a particular
>>>>> common problem case, while other related issues stay unfixed. E.g. if
>>>>> one tries to play 5.1 audio on 7.1 system, with or without this patch:
>>>>> - Front, Center and LFE channels are mapped 1:1, which is correct
>>>>> - Rear (or what mpv calls "Side") source channels are mapped to Side,
>>>>> which is also correct, because it's the Side speakers in the ITU-T 7.1
>>>>> layout, not Rear, which have the nearest position to what Dolby
>>>>> specifies for Surround AC3 speakers.
>>>>> - The true rear channels get a mix between Front and Side, which is
>>>>> clearly incorrect. ITU R-REC-BS.775-3-201208 says that both sets of
>>>>> surround channels should be fed the same signal.
>>>> Regarding that last point, do I understand correctly that the
>>>> recommendation is to duplicate the 5.1 rear(/side) channels to both the
>>>> side and rear channels in 7.1? Doesn't that cause imbalance by
>>>> amplifying the rear channels? Or is it compensated by attenuating the
>>>> signal?
>>> You understood correctly. In my big patch, it is compensated by
>>> attenuating the signal. Anyway, I am going to resubmit it later today
>>> without the half-baked change about the LFE volume.
>> Sorry, I have to do it later. I have too much non-PulseAudio work to do :(
> No problem, I'll postpone reviewing the patch until you've submitted
> the new version. From what I already saw, the general idea behind the
> patch seems good.

Hello Tanu,

thanks for your patience. I have tried to undo the half-baked LFE change 
today, but found two more bugs in my patch that I would rather fix 
before resubmitting it:

1. AUX input channels get sometimes routed to non-AUX output channels 
rather than being dropped. Fixing this right how.

2. Some inconsistencies if either input or output channel map contains 
duplicates. Cannot really fix, because I don't know what's expected.

Could you please help with (2)? In particular, what would be the 
expected channel matrix in the following two cases?

Case A:

front-left, front-right, front-center ->
front-left, front-right, front-center, front-center

I would guess that we should generate two identical front-center output 
channels, both duplicating the front-center input channel with the 
coefficient being 1.0.

Case B:

front-left, front-right, front-left, front-right -> front-left, front-right

Would it be OK if I drop the redundant input channels, i.e. use only the 
first copy of each channel name? Or should I average the redundant 
inputs, or take a sum?

Is there any spec?

Alexander E. Patrakov

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