Implement dynamic crossfade

[michaelwillis]

From issue #19:

Yes, the crossfade calculation are not dynamic right now and they're only checked when the note start. After reading around, this is indeed not what's expected so I'll look into it!

I'm opening this as a separate issue because the main bugs from that issue have been solved.

[davidhealey]

+1 for this. And make it smooth (Aria's implementation is horribly unusable, or I'm doing it wrong).

[michaelwillis]

I made an attempt at implementing this in pull request #26.

[paulfd]

@davidhealey as Michael implemented (and as I would have done it) there is a linear smoothing of the crossfade within a block. There are a couple different options (e.g. multiplicative or with a completely custom shape). If that's not rendering well enough for you we can try to tweak it 🙂

[davidhealey]

Excellent, I'll test it out

[davidhealey]

I'm finding the crossfade choppy. I've tried both .flac and .wav files and found it made no difference. I did select to use a fixed buffer in Carla though and that improved it a little bit. It could of course be me doing something wrong with my SFZ opcodes.

I've uploaded the SFZ along with an mp3 of the output I get - https://www.dropbox.com/sh/nsbaq65jnkd98zq/AABTm8tK5zoPz7MOXJO8x6BTa?dl=0

[alcomposer]

@davidhealey In the SFZ file there is no space in lines 22-34 inclusively- between:
xfout_hiccc1=127volume=-3

It should be:
xfout_hicc1=127 volume=-3

Sfizz reports: [INFO]: [sfizz] Unknown opcodes: 127volume

However I can confirm that in Ardour the crossfade is choppy.

[michaelwillis]

I tested this a bit more thoroughly today. Crossfading in VPO works, but has a little bit of crackle:

https://www.dropbox.com/s/sclkx4h2kqiabjk/vpo_sfizz_crossfade_session_2020-01-19_22.40.mp3

After that I tried switching it to a multiplicative envelop, but with that, the audio cut out entirely after a few moments... @paulfd, any ideas?

[davidhealey]

@davidhealey In the SFZ file there is no space in lines 22-34 inclusively- between:

Oh good catch! I assume it was still working with xfout but was ignoring the volume opcode.

I tested this a bit more thoroughly today. Crossfading in VPO works, but has a little bit of crackle:

What's VPO?

[alcomposer]

@davidhealey VPO = Virtual Playing Orcehstra: http://virtualplaying.com/virtual-playing-orchestra/

[paulfd]

There's a potential solution in 864fe57

I'm not super satisfied from a technical point of view. Just to give context, at least one issue was that when the CC event arrived at a small delay in the block, there would be hardly any smoothing made for the value---the envelopes are linearly interpolated otherwise. After thinking about it and looking around it seems that people mostly add a fixed ramp time, sforzando included. It also seems to me that this ramp should be a function of the block size, otherwise you will still have somewhat sharp edges in the envelopes and thus strange modulation in the signal. I've settled for block size / 2 in the commit, which is a bit high but is smoothest for my ears.

Another approach would be to lowpass-filter the envelope, which is also implied by the _smoothcc opcodes (https://sfzformat.com/modulations/smoothccN). A generic way to tackle this could then be to do coarse ramping by default and count on people to use the smoothing possibilities to clean it up if necessary.

In light of this, I think I should overhaul a bit my envelopes 🙂 Anyway for now tell me if it feels better like that!

[michaelwillis]

The latest is working well for me. It turns out that some of the crackle I experienced was because I had the gain too high and it clipped the signal at the top of the crescendo.

@davidhealey How well does the latest update work for you?

[davidhealey]

It's much better but it's still not buttery smooth. I've added a second audio file to the dropbox folder. It's made from the same ardour session as the previous one, the only thing difference is the build of sfizz (and I fixed the volume opcode).