I think I may be able to solve the clicking after all - I thought it wasn't possible but I seem to have been wrong about the exact cause (I already reduced it by a few dB tonight, just by changing a few values).
Problem:
- For clipping, I process a block of audio, say 4096 samples
- To separate this into multiple threads, I split this block into 2 2048 sample blocks. (They have to be a power of 2).
- Problem: When I merge the two together again, you would get issues at the center. So some (small) amount of overlap is needed.
- Solution: The start and end of the 4096 samples contain near-silence, so I thought it doesn't matter much what you do there. So I basically 'forget' a few samples at the start and end of the 4096 samples block to be able to have some overlap.
In the end, what I do to fix this is just clip the samples at the start and end using 'traditional' clipping, even without oversampling.
Now it turns out that if I make the overlap area smaller, the ticks are softer.
I also found that I did something wrong in the merging code at the center, when I fixed that about half of the clicks disappeared immediately.
Now, I could use the same clipping method that I use for normal processing also for the few samples at the edges. But the amount of power in it is so small that I really don't expect much from it. Also, any audible clicks (as Bojcha just reported) may have come from the wrong merging code.
What I can at least do, it's simple and should be reasonably effective, is to replace the current clipping method by something that takes the stereo and RDS signal into account. I'll add that and I think I'll leave it there unless people really hear clicks with the new version that I'll build tonight.
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It's an option under Advanced Clipper