Hi,
Thanks for your replies.
What I hear is definitely related with the modulation. The artefacts are
audible every time the modulation is applied: manually or automatically (please
not that I have an interpolator for manual parameter changes to avoid abrupt
changes). I think I was already applying an Hermit interpolation. This is my
delay read function.
void IDelay::read(IAudioSample *output)
{
float t = _time+_modulation*_modulationRange;
if (t>(_size-1))
t=_size-1;
float sf;
#if 0
sf = _buffer[int(readIndex(t,0))];
#else
float const y_1= _buffer[int(readIndex(t,-1))];
float const y0 = _buffer[int(readIndex(t,0))];
float const y1 = _buffer[int(readIndex(t,1))];
float const y2 = _buffer[int(readIndex(t,2))];
float const x=readIndex(t,0)-int(readIndex(t,0));
float const c0 = y0;
float const c1 = 0.5f*(y1-y_1);
float const c2 = y_1 - 2.5f*y0 + 2.0f*y1 - 0.5f*y2;
float const c3 = 0.5f*(y2-y_1) + 1.5f*(y0-y1);
sf=((c3*x+c2)*x+c1)*x+c0;
#endif
*output = sf;
}
float IDelay::readIndex(float t, int offset)
{
float index=_writeIndex-t+offset;
if (index<0)
index+=_size;
return index;
}
Thanks,
Regards,
Nuno
> On 19 Mar 2015, at 18:12, David Olofson <da...@olofson.net> wrote:
>
> On Thu, Mar 19, 2015 at 6:15 PM, Nuno Santos <nunosan...@imaginando.pt> wrote:
> [...]
>> If I use interpolation for buffer access I experience less glitch and more
>> alias.
>
> What type of interpolation are you using? I would think you need
> something better than linear interpolation for this. I'd try Hermite.
> That should be sufficient for "slow" modulation, although
> theoretically, you *should* bandlimit the signal as soon as you play
> it back faster than the original sample rate.
>
> For more extreme effects (which effectively means you're sometimes
> playing back audio at a substantially higher sample rate than that of
> your audio stream), you may need a proper bandlimited resampler.
> (Apply a brickwall filter before the interpolation, and/or oversample
> the interpolator.)
>
>
> --
> //David Olofson - Consultant, Developer, Artist, Open Source Advocate
>
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