Ernest

This didn't seem grand enough for a toolbox entry, so here is a brief form announcement. The description and download is here:

http://www.yofiel.com/software/cycling-74-patches/fast-response-limiter

sharing-fast-response-limiter

You're most welcome. It's nothing really complicated, but I never saw a limiter with overlapping windows to reduce response time, so it seemed worth sharing. It'd be easy enough to build one with four or eight overlapping windows and improve response time even more. the same idea could improve quality of compressors and expanders, and when I have time, I'll put together a kit of them.

This much-improved version adjusts for DC bias, applies saturation and distortion, increases response time to 50 msec, and does not require attack or release params. The dc bias removal allows proper adjustment of gain. The 50msec window supports frequencies down to 20Hz. There still can be higher transient peaks within the 50msec window, so it's clipped to +6B, but Im experimenting with adding an immediate response to transients for my synthLab library, which might be released by the time you read this.

        // 0~1 mixes saturation, 

        // 1 = perfect saturation, 

        // >1 adds mirror distortion 

History fclck, period, hi, lo, gain, bias, range, offset, limit;

fclk    = (fclk >1)? 0 : fclk + period;

    if(lo >0){                    // calc dc offset

        gain    = (hi - lo) * .5;

        bias    = neg(gain) - lo;

        gain    = (lo -hi) * .5;

        gain     = (hi - lo) * .5;

        bias     = (hi + lo) * -.5;

    gain = (gain !=0)? min(1/gain, 1) : 0;    // calc limiter factor

    lo = 1000000000;                // reset 

offset = offset + period * (bias - offset);// ramp bias to new val 

limit = limit + period * (gain - limit);// ramp limit to new val 

x = mix(x, tanh(x), 1 -abs(sat));// saturate

out1 = (sat>0)? fold(x *(sat*8 +1), -1, 1) : clip(x, -2, 2);//distort

This much-improved version adjusts for DC bias, applies saturation and distortion, increases response time to 50 msec, and does not require attack or release params. The dc bias removal allows proper adjustment of gain. The 50msec window supports frequencies down to 20Hz. There still can be higher transient peaks within the 50msec window, so it's clipped to +6B, but Im experimenting with adding an immediate response to transients for my synthLab library, which might be released by the time you read this.  

Param sat; 	// 0 = limit only, 
		// 0~1 mixes saturation, 
		// 1 = perfect saturation, 
		// >1 adds mirror distortion 
History fclck, period, hi, lo, gain, bias, range, offset, limit;
// set up limiter clock
period  = 1 / mstosamps(50);
fclk	= (fclk >1)? 0 : fclk + period;
if (change(fclk) > 0.5) { 
	if(lo >0){					// calc dc offset
		gain	= (hi - lo) * .5;
		bias	= neg(gain) - lo;
} else if (hi <= 0){
		gain	= (lo -hi)  * .5;
		bias	= gain      + lo;
	} else {
		gain 	= (hi - lo) *  .5;
		bias 	= (hi + lo) * -.5;
	}
	gain = (gain !=0)? min(1/gain, 1) : 0;	// calc limiter factor
	lo =  1000000000;				// reset 
	hi = -1000000000;
}
hi     = max(hi, in1);
lo     = min(lo, in1);
offset = offset + period * (bias - offset);// ramp bias to new val 
limit  = limit + period * (gain - limit);// ramp limit to new val 
x      = (in1 + offset) * limit;
x      = mix(x, tanh(x), 1 -abs(sat));// saturate
out1   = (sat>0)? fold(x *(sat*8 +1), -1, 1) : clip(x, -2, 2);//distort

An ideal limiter with optional saturation and distortion: I think I got it! Better than a filter based one, because it at most distorts half a wave cycle once every 50msec. What do you know. Something genuinely new that actually works, at least I think it works after half an hour of testing, but I'll keep hammering it for a while just to makes sure. I've been running it 4x oversampled, but maybe that's not so necessary with this redesign, except for reducing distortion on the first half wave when a changed signal exceeds the prior limiter level. 

//---------------------------------------------------------------
saturator6(in1, sat, clk, period) { 
// in1        : input in any range
// sat        : saturation level, 0~1
// clk      : zero crossing causes level resampling, typ. 20Hz.
// period     : period of clk in msec.
// Return:       Unity gain output.
    Data qtanh(16384);
    History hi, lo, peak, gain, amp, bias;
    if (change(clk) > 0) { 
        bias, gain, amp = biasGain(in1, lo, hi);
        lo       =  999999999;        // reset 
        hi, peak = -999999999;
    }
    lo     = min(lo, in1);        // remember min, max, peak
    hi     = max(hi, in1);
    peak = max(peak, max(lo, hi));
    flag = 0;
    // if transient peak >+/-1 between clks, 
    // increase bias & gain at once 
    if (peak > amp + bias) {        
        bias, gain, amp = biasGain(in1, lo, hi);
        flag = 1;
    }
    L, C, R = mixer3(sat);
    // add bias for both left and right channels
    signal = in1 + ramp1(bias, period, 1);
    // left channel: limiter. Apply adjusted gain. 
    left   = L * signal * ramp1(gain, period, 1);
    // right channel: saturator. Apply tanh and mirror distortion.
    right  = tanh(in1 * 4); 
    right  = (sat > 0)? fold(right *(R *8 +1), -1, 1) : C * right;
    return left + right;
}
//---------------------------------------------------------------
// 3-way linear mixer, returns gain for three channels
mixer3(in1){ 
// x     : -1= chan1, 0 = chan2, 1 = chan3
//return : gain for three channels in range 0~1 
    if(in1 >0) { return 0, 1 -in1, in1; } 
     else { return abs(in1), 1 +in1, 0; }
}
//---------------------------------------------------------------
// ramps to new val at rate set by incr
ramp0(in1, incr){
    History prev;
    prev = prev + incr * (in1 -prev);        
    return prev;
}
//---------------------------------------------------------------
// ramps to new val, or sets to in1 at once if flag=1
ramp1(in1, incr, flag){
    History prev;
    prev = (flag ==1)? in1 : prev + incr * (in1 -prev);        
    return prev;
}
//---------------------------------------------------------------
//gain and bias of windowed signal, used by limiter and saturator
biasGain(in1, lo, hi){
// lo    : min window value
// hi    : max window value
// return: bias, amp, and 1/amp as gain to apply for unity output 
    amp, bias = 0;
    if(lo >0){                // calc dc offset
        amp        = (hi - lo) * .5;
        bias    = neg(amp) - lo;
    } else if (hi <= 0){
        amp        = (lo -hi)  * .5;
        bias    = amp       + lo;
    } else {
        amp     = (hi - lo) *  .5;
        bias     = (hi + lo) * -.5;
    }
    gain = (amp ==0)? 0 : min(1/amp, 1);    // calc limiter factor
    return bias, gain, amp;
}
//---------------------------------------------------------------
MAIN
//---------------------------------------------------------------
Data qtanh(16384);
Param sat, finit;
if(finit==0){
    // for limter clock, captures peak of waves down to 25Hz
    period = 1 / mstosamps(50);    
    for (x = 0; x <16384; x +=1){
        y = (x==0)? -4 : (x/16384 * 8) -4;
        qtanh.poke(tanh(y), x);
    }    finit    = 1;
}
// set up limiter clock
clk = (fclk >1)? 0 : clk + period;

out1 = saturator5(in1, ramp0(sat, period), clk, period);

An ideal limiter with optional saturation and distortion: I think I got it! Better than a filter based one, because it at most distorts half a wave cycle once every 50msec. What do you know. Something genuinely new that actually works, at least I think it works after half an hour of testing, but I'll keep hammering it for a while just to makes sure. I've been running it 4x oversampled, but maybe that's not so necessary with this redesign, except for reducing distortion on the first half wave when a changed signal exceeds the prior limiter level. 

//---------------------------------------------------------------
saturator6(in1, sat, clk, period) { 
// in1		: input in any range
// sat		: saturation level, 0~1
// clk  	: zero crossing causes level resampling, typ. 20Hz.
// period 	: period of clk in msec.
// Return: 	  Unity gain output.
	Data qtanh(16384);
	History hi, lo, peak, gain, amp, bias;
	if (change(clk) > 0) { 
		bias, gain, amp = biasGain(in1, lo, hi);
		lo       =  999999999;		// reset 
		hi, peak = -999999999;
	}
	lo	 = min(lo, in1);		// remember min, max, peak
	hi	 = max(hi, in1);
	peak = max(peak, max(lo, hi));
	flag = 0;
	// if transient peak >+/-1 between clks, 
	// increase bias & gain at once 
	if (peak > amp + bias) {		
		bias, gain, amp = biasGain(in1, lo, hi);
		flag = 1;
	}
	L, C, R = mixer3(sat);
	// add bias for both left and right channels
	signal = in1 + ramp1(bias, period, 1);
	// left channel: limiter. Apply adjusted gain. 
	left   = L * signal * ramp1(gain, period, 1);
	// right channel: saturator. Apply tanh and mirror distortion.
	right  = tanh(in1 * 4); 
	right  = (sat > 0)? fold(right *(R *8 +1), -1, 1) : C * right;
	return left + right;
}
//---------------------------------------------------------------
// 3-way linear mixer, returns gain for three channels
mixer3(in1){ 
// x     : -1= chan1, 0 = chan2, 1 = chan3
//return : gain for three channels in range 0~1 
	if(in1 >0) { return 0, 1 -in1, in1; } 
 	else { return abs(in1), 1 +in1, 0; }
}
//---------------------------------------------------------------
// ramps to new val at rate set by incr
ramp0(in1, incr){
	History prev;
	prev = prev + incr * (in1 -prev);		
	return prev;
}
//---------------------------------------------------------------
// ramps to new val, or sets to in1 at once if flag=1
ramp1(in1, incr, flag){
	History prev;
	prev = (flag ==1)? in1 : prev + incr * (in1 -prev);		
	return prev;
}
//---------------------------------------------------------------
//gain and bias of windowed signal, used by limiter and saturator
biasGain(in1, lo, hi){
// lo    : min window value
// hi    : max window value
// return: bias, amp, and 1/amp as gain to apply for unity output 
	amp, bias = 0;
	if(lo >0){				// calc dc offset
		amp		= (hi - lo) * .5;
		bias	= neg(amp) - lo;
	} else if (hi <= 0){
		amp		= (lo -hi)  * .5;
		bias	= amp       + lo;
	} else {
		amp 	= (hi - lo) *  .5;
		bias 	= (hi + lo) * -.5;
	}
	gain = (amp ==0)? 0 : min(1/amp, 1);	// calc limiter factor
	return bias, gain, amp;
}
//---------------------------------------------------------------
MAIN
//---------------------------------------------------------------
Data qtanh(16384);
Param sat, finit;
if(finit==0){
	// for limter clock, captures peak of waves down to 25Hz
	period = 1 / mstosamps(50);	
	for (x = 0; x <16384; x +=1){
		y = (x==0)? -4 : (x/16384 * 8) -4;
		qtanh.poke(tanh(y), x);
	}	finit	= 1;
}
// set up limiter clock
clk = (fclk >1)? 0 : clk + period;

out1 = saturator5(in1, ramp0(sat, period), clk, period);

[sharing] fast-response limiter