Playtime: Improve latency compensation when recording

[helgoboss]

Quantized audio recordings work nicely even when using high buffer sizes. But with quantized MIDI recordings, MIDI events end up at the wrong position.

[helgoboss]

Should probably have two behaviors:

a) If input monitoring is disabled (auto or on): Compensate for latency (audio_output_latency + block_size)
b) if input monitoring is enabled (off): Don't compensate for latency at all (because player probably adjusts his playing based on what he hears already)

Consider doing this distinction for audio as well!

[helgoboss]

Enough tuning for now. Here's how it works after those changes:

Input monitoring	Start timing	Kind	Compensation	Comment
Off	Immediately	Any	Off
Off	Quantized	Audio	Audio output latency + audio input latency
Off	Quantized	MIDI (normal)	Audio output latency + block size (new)	This is the main change and turns MIDI recording at high buffer sizes from a horrible to a pleasant experience.
Off	Quantized	MIDI (overdub)	Audio output latency + block size + PDC read-ahead (new)	Results not too good when using high buffer sizes, but okay for now.
On	Any	Audio	Audio input latency (new, was previously also audio output latency)	This change makes things more consistent with MIDI. See FAQ below.
On	Any	MIDI (any)	Off

FAQ

When does this matter?

In general, those things should only matter when using high buffer sizes, since only then the delays introduced by latency become musically sensible.

Why compensate output latency only if input monitoring is off?

When input monitoring is off (in the DAW), I assume that the user uses some kind of zero-latency monitoring. In case of audio, this might be direct monitoring via audio interface or just listening to the instrument/voice itself. In case of MIDI, this might be an external hardware synthesizer with Local Mode being On or no monitoring at all (just pressing the keys at the right moment). In that case, what counts in terms of timing is the actual key press (keyboard), strum (guitar), beat (drums), etc. This needs output latency compensation!

When input monitoring is on (in the DAW), I assume that the player adjusts his playing according to what he hears coming out from the DAW and expects that this is the timing that ends up in the recording. This means that output latency compensation is not necessary. Having input monitoring on in the DAW is usually only bearable when using low buffer sizes, otherwise it's super confusing.