add ba.downSampleCV

[DBraun]

Here is a polyphonic demo:

import("stdfaust.lib");
import("basics.lib");

//--------------------------`(ba.)downSampleCV`---------------------------
//
// A version of `ba.downSample` where the frequency parameter has
// been replaced by an `amount` parameter that is in the range zero
// to one. WARNING: this function doesn't change the rate of a
// signal, it just holds samples...
//
// #### Usage
// ```
// _ : downSampleCV(amount) : _
// ```
// Where:
//
// * `amount`: The amount of down-sampling to perform [0..1]
//-----------------------------------------------------------------------
downSampleCV(amt) = sAndH(hold)
with {
    // If amt is 0, then freq should be ma.SR/2.
    // If amt is 1, then freq should be 491.
    // 491 is derived from listening to the Serum synthesizer.
    freq = amt : it.remap(0, 1, hz2midikey(ma.SR/2), hz2midikey(491)) : midikey2hz;
    hold = time%int(ma.SR/freq) == 0;
};

process = os.m_osccos(freq)*en.adsr(.01, 1, 1, .1, gate) : downSampleCV(amt) * .8 <: _, _
with {
    freq = hslider("freq", 440, 10, 20000, 1);
    gain = hslider("gain", 0, 0, 1, .01);
    gate = hslider("gate", 0, 0, 1, .01);
    amt = hslider("Downsample Amount", 0, 0, 1, .01);
};