On 9/24/19 4:26 PM, Paul Davis wrote:
On Tue, Sep 24, 2019 at 12:38 PM Johannes Lorenz <j.s...@lorenz-ho.me
<mailto:j.s...@lorenz-ho.me>> wrote:
Counting zero crossings prevents
clicking on lower notes, and it makes higher notes more punchy.
There's fundamentally no such thing as a zero crossing. You might have
two samples on either side of zero, but you still don't have a sample
*at* zero, so in the general case, truncating one of them to zero and
starting/ending there is still going to give you distortion and/or
noise. Obviously there may be cases where one of them is close enough to
zero for this not to be be an issue, but it's not a general method.
Ardour applies declick fades every time the transport starts and stops.
You can read about how we do it here:
https://github.com/Ardour/ardour/blob/master/libs/ardour/ardour/disk_reader.h#L135
https://github.com/Ardour/ardour/blob/master/libs/ardour/disk_reader.cc#L1445
https://github.com/Ardour/ardour/blob/master/libs/ardour/amp.cc#L163
Hi Paul. Thanks, I was going to mention that.
We had a similar conversation a few years ago when I was adding
anti-zipper noise to MusE, and I inquired about zero-crossing methods.
I replied that TV and amplifier electronic volumes use zero-crossing,
so why not use it?
But I conceded the very point you mention above, ie. where exactly is
the crossing point.
And it is dependent on frequency so you get a different attack result
each time.
In a TV or amp volume chip it's OK but here, meh...
So in the end, looking at the code given above, I can see I did much
the exact same thing as Ardour, using a fixed coefficient value
driven by time passage (sample rate).
Cheers.
Tim.
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