Enable echo cancellation by default

[Krzmbrzl]

Now that the echo canceller has been fixed, it is time to default-enable
echo cancelling. As multi-channel cancelling is more CPU intensive, we
default to mixed channel cancellation.

Don't enable it on MacOS though as right now we don't support echo
cancellation for that platform.

Closes: #4178

Changelog:

| Improved: Echo cancellation now enabled by default

[TerryGeng]

Since echo cancellation only works for some platform (where you can hijack the system audio output as your echo source), did this change take this fact into account?

I'm running mumble at Mac, and I'm afraid that this option will be marked as on in the settings window but is off in the background, and since this option will be disabled by

mumble/src/mumble/AudioConfigDialog.cpp

Lines 410 to 420 in 803ef7f

	if (air->canEcho(outputInterface)) {
	qcbEcho->setEnabled(true);
	qcbEcho->setToolTip(QObject::tr("If enabled this tries to cancel out echo from the audio stream.\n"
	"Mixed echo cancellation mixes all speaker outputs in one mono stream and passes that stream to "
	"the echo canceller, while multichannel echo cancellation passes all audio channels to the echo canceller directly.\n"
	"Multichannel echo cancellation requires more CPU, so you should try mixed first"));
	} else {
	qcbEcho->setEnabled(false);
	qcbEcho->setToolTip(QObject::tr("Echo cancellation is not supported for the interface "
	"combination \"%1\" (in) and \"%2\" (out).").arg(air->name).arg(outputInterface));
	}

, it will look like this option is forced to be on, but actually that is not the case in the background.

Update: This worry confirmed by seeing that

mumble/src/mumble/AudioConfigDialog.cpp

Lines 167 to 172 in 803ef7f

	int echo = 0;
	if (r.bEcho)
	echo = r.bEchoMulti ? 2 : 1;
	loadComboBox(qcbEcho, echo);
	}

Where this checkbox is initialized with no check by calling canEcho function.

Proposed solution:
add

loadComboBox(qcbEcho, 0); 

after L417.

[fedetft]

I see a bEchoMulti = true; in Settings, won't this enable multichannel echo cancellation by default?

[TerryGeng]

I see a bEchoMulti = true; in Settings, won't this enable multichannel echo cancellation by default?

I think now that bEcho is true by default, we need to set bEchoMulti to false.

[Krzmbrzl]

@TerryGeng yes you are right. I forgot about the Mac situation.

@fedetft you are also correct. I'll have to set that to false then. I don't even know why this would be enabled by default why echo cancelling itself is disabled by default 🤷

[Krzmbrzl]

Both should be fixed now

[TerryGeng]

Thanks for the quick reply! Hmmmmm.... It looks like it is not only the problem of mac.
ALSA -> not supported
ASIO -> supported
CoreAudio(Mac) -> not supported
JACK -> not supported
OSS -> not supported
PortAudio -> not supported
PulseAudio -> it depends
WSAPI -> it depends

SInce whether echo cancellation is supported depends on the Audio backend used, not just the OS. I suggest that adopting my proposed way:

Add loadComboBox(qcbEcho, 0); after L417 of

mumble/src/mumble/AudioConfigDialog.cpp

Lines 410 to 420 in 803ef7f

	if (air->canEcho(outputInterface)) {
	qcbEcho->setEnabled(true);
	qcbEcho->setToolTip(QObject::tr("If enabled this tries to cancel out echo from the audio stream.\n"
	"Mixed echo cancellation mixes all speaker outputs in one mono stream and passes that stream to "
	"the echo canceller, while multichannel echo cancellation passes all audio channels to the echo canceller directly.\n"
	"Multichannel echo cancellation requires more CPU, so you should try mixed first"));
	} else {
	qcbEcho->setEnabled(false);
	qcbEcho->setToolTip(QObject::tr("Echo cancellation is not supported for the interface "
	"combination \"%1\" (in) and \"%2\" (out).").arg(air->name).arg(outputInterface));
	}

This will essentially check with the current audio setup to determine whether echo cancellation can be enabled, and then set the checkbox. So we don't have to worry that we freeze our combo box when it is set to "on".

[Krzmbrzl]

@TerryGeng sounds good to me. I think though that this should be a separate PR. Since you brought it up: Do you want to create said PR to also receive the glory for the change/fix? :D