channel-major vs frame-major?

[ssfrr]

Given that there are likely a number of breaking changes coming down the pike, this might be a good time to think about whether keeping each channel's data contiguous is the right design.

Pros of channel-major:

• operations that run across an individual channel are fast (memory locality and SIMD-able)
• We usually think of Vectors as being vertical, which means that 1D SampleBufs and 1-channel 2D (Nx1) SampleBufs map onto each other. That said, I've always found that distinction to be a bit awkward anyways.

Pros of frame-major:

• Keeping each frame contiguous would be more compatible with streaming data, which is fundamentally interleaved
• time-slices of a multichannel signal would be contiguous

There are probably other pros and cons I'm not thinking of right now. I just wanted to mark this to see if anyone had thoughts, given that there's a bit of activity lately.

cc @mchitre @haberdashPI

[haberdashPI]

I am also currently using channel-major by default in SignalOperators, and am leaning towards moving to frame-major by default. I have almost identical reasons for it though, and no new insights to add here.

[ssfrr]

Thanks, it's nice to hear some confirmation.

Another consideration is that it's kind of nice that for the frame-major orientation the memory layout is the same between a Array and a Vector{NTuple}, which is another reasonable way to represent multichannel signals, and lets you iterate frames easily.

[mchitre]

My vote for frame-major. In my experience, reading a single channel chunk (many frames) of data for processing is a more common requirement.