Re: [Csnd-dev] [EXTERNAL] [Csnd-dev] long-standing diskin/diskin2 issue

Well since no one answered earlier, I went with option 2, which wasn’t too difficult to implement and also
it allowed me to fix the “inconsistent channels” init error which always bugged me as a half-assed implementation.

https://github.com/csound/csound/pull/2128

I think both would solutions could potentially break code. Solution 2 won’t make anyone’s code fail like
solution 1. It’s also possible to implement solution 1 on top of this (it’s independent of my fix).

========================
Prof. Victor Lazzarini
Maynooth University
Ireland

> On 12 Apr 2025, at 10:25, Rory Walsh <[email protected]> wrote:
> 
> *Warning*
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> I think option 1 is the best, even though there is a chance that this will break existing instruments. 
> 
> On Fri, 11 Apr 2025 at 10:58, Victor Lazzarini <[email protected]> wrote:
> Hi everyone, 
> 
> some advice needed here.
> While marking some student work, I came across an issue in diskin/diskin2 that seems to be long standing
> and maybe someone might have come across this and dismissed it.
> 
> The code I was looking at was reading a stereo file peaking near 0dbfs, but the output from diskin was
> double that (and so causing samples out of range). After several checks, I figured the problem was
> with diskin. Then I noticed the code was using the same variable for left and right
> 
> asig, asig diskin …
> 
> so I went to look at the sources and saw that diskin does some summing to these variables as
> part of its process. Normally, you would think that it would just overwrite them, but it is
> actually using them for some internal buffering. The result is that if the same variable is used,
> we get the strange effect of the two file channels being mixed up (and possibly other effects depending
> on diskin/diskin2 parameters).
> 
> So I am in two minds about this:
> 
> 1 - it is user error: we should throw an init error.
> 
> 2 - it is not user error and diskin is not behaving properly.
> 
> I don’t actually like the fact the opcode uses the output variable for buffering, but we probably have
> similar cases elsewhere. The simplest thing is to treat it as 1 and document it in the manual.
> Interestingly it is a similar issue I have encountered with pass-by-reference UDOs 
> (see https://github.com/csound/csound/issues/2061)
> 
> What do you think?
> ========================
> Prof. Victor Lazzarini
> Maynooth University
> Ireland
>