AM pitchshifter
This plugin works by running a single write pointer (monotonic) and two read pointers (pitchscaled) over a ringbuffer.
The output is faded between the two readpointers according to the sine of the distance from the write pointer. The design is based on the mechanism of a mechanical pitchshifter I saw in the Gemeentemuseum in Den Haag, though I'm sure it is a common enough algorithm.
delay);
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7) {
size_tmp = 5;
} else if (size_tmp < 1) {
size_tmp = 1;
}
plugin_data->last_size = size;
/* Calculate the ringbuf parameters, the magick constants will need
* to be changed if you change DELAY_SIZE */
delay_mask = (1 << (size_tmp + 6)) - 1;
delay_ofs = 1 << (size_tmp + 5);
}
for (pos = 0; pos < sample_count; pos++) {
float out = 0.0f;
if (count++ > 14) {
float tmp;
count = 0;
tmp = 0.5f * (float)((rptr.part.in - wptr + delay_ofs/2) &
delay_mask) / (float)delay_ofs;
tmp = sinf(M_PI * 2.0f * tmp) * 0.5f + 0.5f;
gain_inc = (tmp - gain) / 15.0f;
}
gain += gain_inc;
delay[wptr] = input[pos];
/* Add contributions from the two readpointers, scaled by thier
* distance from the write pointer */
i = rptr.part.in;
out += cube_interp((float)rptr.part.fr * 0.0000152587f,
delay[(i - 1) & delay_mask], delay[i],
delay[(i + 1) & delay_mask],
delay[(i + 2) & delay_mask]) * (1.0f - gain);
i += delay_ofs;
out += cube_interp((float)rptr.part.fr * 0.0000152587f,
delay[(i - 1) & delay_mask], delay[i & delay_mask],
delay[(i + 1) & delay_mask],
delay[(i + 2) & delay_mask]) * gain;
buffer_write(output[pos], out);
/* Increment ringbuffer pointers */
wptr = (wptr + 1) & delay_mask;
rptr.all += om.all;
rptr.part.in &= delay_mask;
}
plugin_data->rptr.all = rptr.all;
plugin_data->wptr = wptr;
plugin_data->delay_mask = delay_mask;
plugin_data->delay_ofs = delay_ofs;
plugin_data->last_gain = gain;
plugin_data->count = count;
plugin_data->last_inc = gain_inc;
*(plugin_data->latency) = delay_ofs/2;
]]>
Pitch shift
The multiple of the output pitch, eg. 2.0 will increase the pitch by one octave.
Buffer size
The order of magnitude of the buffer size. Small buffers will sound fluttery, large buffers will have flangy sounding echos.
I recommend a buffer size of 3 for a reasonable compromise, with wideband material at around 48KHz. For drums you might have to lower it, and for voiced background noises it can go higher.
Input
Output
latency