based on STK 4.1.3 source code by Perry R. Cook and Gary P. Scavone, 1995 - 2002.

SynthDef(\flute, { arg out=0, gate=1, freq=440, amp=1.0, endReflection=0.5, jetReflection=0.5, jetRatio=0.32, noiseGain=0.15, vibFreq=5.925, vibGain=0.0, outputGain=1.0;

	var adsr = (amp*0.2) + EnvGen.ar(Env.adsr(0.005, 0.01, 1.1, 0.01), gate, doneAction: 2);
	var noise = WhiteNoise.ar(noiseGain);
	var vibrato = SinOsc.ar(vibFreq, 0, vibGain);

	var delay = (freq*0.66666).reciprocal;
	var lastOut = LocalIn.ar(1);
	var breathPressure = adsr*Mix([1.0, noise, vibrato]);
	var filter = LeakDC.ar(OnePole.ar(lastOut.neg, 0.7));
	var pressureDiff = breathPressure - (jetReflection*filter);
	var jetDelay = DelayL.ar(pressureDiff, 0.025, delay*jetRatio);
	var jet = (jetDelay * (jetDelay.squared - 1.0)).clip2(1.0);
	var boreDelay = DelayL.ar(jet + (endReflection*filter), 0.05, delay);
	LocalOut.ar(boreDelay);
	Out.ar(out, 0.3*boreDelay*outputGain);
}).store;

SynthDef(\blowbotl, { arg out=0, amp=1.0, freq=440, rq=0.0, gate=1, noise=0.0, vibFreq=5.2, vibGain=0.0;
	var lastOut = LocalIn.ar(1);
	var adsr = amp*EnvGen.ar(Env.adsr(0.005, 0.01, 1.0, 0.010), gate, doneAction: 2);
	var vibrato = SinOsc.ar(vibFreq, 0, vibGain);
	var pressureDiff = (adsr+vibrato) - lastOut;
	var jet = (pressureDiff * (pressureDiff.squared - 1.0)).clip2(1.0);
	var randPressure = WhiteNoise.ar(noise)*adsr*(1.0 + pressureDiff);
	
	var resonator = Resonz.ar(adsr+randPressure - (jet*pressureDiff), freq, rq);
	LocalOut.ar(resonator);
	Out.ar(out, LeakDC.ar(resonator));
}).store

SynthDef(\bowed, { arg out=0, amp=1.0, gate=1, freq=420, bowOffset = 0.0, bowSlope = 0.5, bowPosition = 0.75, vibFreq=6.127, vibGain=0.0;
	var betaRatio = 0.027236 + (0.2*bowPosition);
	var baseDelay = freq.reciprocal;
	var lastOut = LocalIn.ar(2);
	var vibrato = SinOsc.ar(vibFreq, 0, vibGain);
	var neckDelay = baseDelay*(1.0-betaRatio) + (baseDelay*vibrato);
	var neck = DelayL.ar(lastOut[0], 0.05, neckDelay);
	var bridge = DelayL.ar(lastOut[1], 0.025, baseDelay*betaRatio);
	var stringFilter = OnePole.ar(bridge*0.95, 0.55);
	var adsr = amp*EnvGen.ar(Env.adsr(0.02, 0.005, 1.0, 0.01), gate, doneAction: 2);
	var bridgeRefl = stringFilter.neg;
	var nutRefl = neck.neg;
	var stringVel = bridgeRefl + nutRefl;
	var velDiff = adsr - stringVel;
	var slope = 5.0 - (4.0*bowSlope);
	var bowtable = (( ((velDiff+bowOffset)*slope) + 0.75 ).abs ).pow(-4).clip(0, 1);
	var newVel = velDiff*bowtable;
	LocalOut.ar([bridgeRefl, nutRefl] + newVel);
	Out.ar(out, Resonz.ar( bridge*0.5, 500, 0.85 ) );
}, [\ir, 0,0, 0, 0, 0, 0, 0, 0]).store;

SynthDef(\voicform, { arg out=0, gate=1, freq=440, amp=1.0, voiceGain=1.0, noiseGain=0.0, sweepRate=0.001;
	
	var voiced = Pulse.ar(freq, 0.1, voiceGain);
	var onezero = OneZero.ar(voiced, -0.9);
	var onepole = OnePole.ar(onezero, 0.97 - (amp*0.2));
	var noise = WhiteNoise.ar(noiseGain*0.1);
	var excitation = onepole + noise;

	var ffreqs = Control.names([\ffreq]).kr([770, 1153, 2450, 3140]);
	var fradii = Control.names([\bw]).kr([0.950, 0.970, 0.780, 0.8]);
	var famps = Control.names([\gain]).kr([1.0, 0.355, 0.0355, 0.011]);
	
	var filters = TwoPole.ar(excitation, Lag.kr(ffreqs, sweepRate), Lag.kr(fradii, sweepRate), Lag.kr(famps, sweepRate) );
	
	Out.ar(out, amp*Mix(filters) );
}).store;

Note: you can try using voicform with this class file: Phonemes
Example usage:

x = Synth(\voicform);
x.set(\sweepRate, 0.5);
i=0;

(
    i = i+1;
    a = Phonemes.parameter(i).flop;
    b = Phonemes.gain(i);
    Phonemes.string(i).postln;
    x.setn(\ffreq, a[0]);
    x.setn(\bw, 1-a[1]);
    x.setn(\gain, a[2].dbamp);
    x.set(\voiceGain, b[0]);
    x.set(\noiseGain, b[1]);
    x.set(\freq, exprand(200, 800) );
)