record and broadcast microphone inputs with latency compensation

[Be]

It would be nice if Mixxx could record microphone and auxiliary inputs exactly sample aligned with the master output without sending the mixed signal to the master output sound card. This would allow users to make use of direct monitoring on sound cards while playing to avoid the latency of routing the audio into the computer and back out and still record their live mixes as heard.

[Daniel Schürmann (daschuer)]

Sorry, I do not understand what you are suggesting.

Can you describe which signal is passed by Aux and Mic? A picture or ASCII art would be nice as well.

[Be (be.ing)]

I have attached a sketch of the signal path. It would be nice if Mixxx's recording compensated for the input latency to the computer.

[Daniel Schürmann (daschuer)]

Ah I understand now, thank you. This feature would also be great for broadcasting users.

We already have the option to pass the Talkover channel to Broadcasting and recording only.
The only part that is missing is to delay the master stream that is passed to the sidechain.

It looks like this is a reasonable feature. But how can find out the this delay value delay?

If you are planning to do this here some hints:
We need a new engine delay like this:
https://github.com/mixxxdj/mixxx/blob/master/src/engine/enginemaster.cpp#L101
The delay has to placed here;
https://github.com/mixxxdj/mixxx/blob/master/src/engine/enginemaster.cpp#L512
like:
https://github.com/mixxxdj/mixxx/blob/master/src/engine/enginemaster.cpp#L581
We have to make sure, that the original master buffer is not touched.

[Be (be.ing)]

>It looks like this is a reasonable feature. But how can find out the this delay value delay?

I think that can only be determined by empirical measurement with a cable running from the sound card's output back to its input. The jack_delay tool can measure the roundtrip latency with such a configuration. If Mixxx is run with JACK's -I and -O parameters set, that can be used to specify the delay. Otherwise, there could be a place to specify it in the preferences.

[Be (be.ing)]

https://github.com/mixxxdj/mixxx/pull/1279

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/8477