At Wed, 29 Feb 2012 11:45:40 +0100, David Henningsson wrote:
On 02/29/2012 10:56 AM, Takashi Iwai wrote:
At Wed, 29 Feb 2012 10:21:35 +0100, David Henningsson wrote:
On 02/28/2012 08:42 PM, Takashi Iwai wrote:
At Tue, 28 Feb 2012 19:11:15 +0100, David Henningsson wrote:
On 02/28/2012 04:20 PM, Takashi Iwai wrote:
> I'm talking about recording an internal mic in *stereo*, as I just wrote > below. Or don't you agree that is a valid and probably fairly common use > case?
Well, when you record it in stereo, and play it back, then you hear the sound without problem.
That could definitely be questioned: depending on the distance between speakers when you're finally playing it back, you might lose bass frequencies [1]. (That said, I'm not sure how much bass these mics pick up anyway.)
Well, it might be, in the worst case.
The problem happens only when you sum the left and right signals into mono. Thus, as long as the stream is handled as stereo, it could be passed as is, although it's not optimal.
So the official recommendation is that summing left and right to make a mono signal, is to be considered an invalid operation?
It's not invalid in general but invalid for this digital mic. That's the only point. Thus, avoiding summing only for known bad devices is also a way to go, IMO. It'd work more or less stably. OTOH, muting the right reduces the risk but it also has a problem of the lower volume and the lack of right signal in stereo streams, both of which aren't easily avoided.
So we need to find some point of compromise...
Avoiding summing only for known bad devices and only when mixer is set to capture Internal Mic, is a quite complex condition that would have to implemented in not only PulseAudio, but every application using ALSA directly. (Well, and wants to either sum, or to avoid loss of bass and strange stereo effects.)
As mentioned, ALSA-native "default" doesn't sum for mono signals. It's not optimal for stereo, yeah, but better than summing blindly.
The lower volume problem is also an argument only if you want to sum the signal; so in this case it's lower volume against a cancelled signal altogether, in which case lower volume is better.
Of course. But my comparison is "pick up only left" vs "sum but right-mute". In the latter case, the lower volume happens also in stereo streams (as a total volume), too.
That leaves the lack of right signal in stereo streams, as a disadvantage with the proposed solution. In which use cases do you think this is a problem?
Honestly, I don't know. It sounds really like a user's preference to me.
Ok.
BTW, it'd be possible to give some offsets to the internal mic capture volume to compensate the lack of a stream.
Hmm...could you elaborate on this? What type of offsets are you referring to?
cx5051 has separate capture volumes and I thought of adding a base dB offset (+6dB) only to digital-mic so that it'll be higher than other inputs.
Takashi