public void SetRelease(double releaseMs)
{
ReleaseMs = releaseMs;
double dbDecayPerSample = -60 / (ReleaseMs / 1000.0 * Fs);
fastDecay = Utils.Db2Gain(dbDecayPerSample);
}
public EnvelopeFollower(double fs, double releaseMs)
{
Fs = fs;
double ts = 1.0 / fs;
inputFilter = new Butterworth(fs);
inputFilter.Parameters[Butterworth.P_ORDER] = 2;
inputFilter.Parameters[Butterworth.P_CUTOFF_HZ] = InputFilterCutoff;
inputFilter.Update();
var emaAlpha = Utils.ComputeLpAlpha(EmaFc, ts);
double slowDbDecayPerSample = -60 / (3000 / 1000.0 * fs);
slowDecay = Utils.Db2Gain(slowDbDecayPerSample);
SetRelease(releaseMs);
sma = new Sma((int)(fs * SmaPeriodSeconds));
ema = new Ema(emaAlpha);
movementLatch = new EmaLatch(0.005, 0.2); // frequency dependent, but not really that critical...
triggerCounterTimeoutSamples = (int)(fs * TimeoutPeriodSeconds);
holdAlpha = Utils.ComputeLpAlpha(HoldSmootherFc, ts);
}
public void Run()
{
/*var pm = new PlotModel();
* var xs = Enumerable.Range(0, 1000).Select(x => x / 1000.0).Select(x => -100 + x * 100).ToArray();
* var ys1 = xs.Select(x => Compress(x, ThresholdDb, UpperSlope, 3, true)).ToArray();
* var ys2 = xs.Select(x => Compress(x, ThresholdDb + 6, LowerSlope, 3, true)).ToArray();
*
* pm.AddLine(xs, ys1);
* pm.AddLine(xs, ys2);
* pm.Show();
*/
var pm = new PlotModel();
pm.Axes.Add(new LinearAxis {
Position = AxisPosition.Left, Key = "L"
});
pm.Axes.Add(new LinearAxis {
Position = AxisPosition.Right, Key = "R"
});
var follower = new EnvelopeFollower(48000, 20);
var expander = new Expander();
var slewLimiter = new SlewLimiter(48000);
follower.SetRelease(ReleaseMs);
slewLimiter.UpdateDb60(2.0, ReleaseMs);
expander.Update(ThresholdDb, ReductionDb, UpperSlope);
var signalValues = new List <double>();
var followerValues = new List <double>();
var gainValues = new List <double>();
var rand = new Random();
Func <double> random = () => 2 * rand.NextDouble() - 1;
double decay = 1.0;
for (int i = 0; i < 20000; i++)
{
var x = (Math.Sin(i / fs * 2 * Math.PI * 300) + random() * 0.4) * decay;
decay *= 0.9998;
if (i < 1000)
{
x = random() * 0.001;
}
else if (i > 12000)
{
x = random() * 0.001;
}
signalValues.Add(x);
follower.ProcessEnvelope(x);
var env = follower.GetOutput();
followerValues.Add(env);
expander.Expand(Utils.Gain2Db(env));
var gainDb = expander.GetOutput();
gainDb = slewLimiter.Process(gainDb);
var gain = Utils.Db2Gain(gainDb);
gainValues.Add(gain);
}
var signalLine = pm.AddLine(signalValues);
signalLine.Title = "Signal";
signalLine.YAxisKey = "R";
//pm.AddLine(followerValues.Select(Utils.Gain2Db)).Title = "followerValues";
pm.AddLine(gainValues.Select(Utils.Gain2Db)).Title = "gainValues";
pm.Show();
}
public void ProcessEnvelope(double val)
{
double combinedFiltered;
double decay;
// 1. Rectify the input signal
val = Math.Abs(val);
// 2. Band pass filter to ~ 100hz - 2Khz
//lpValue = lpAlpha * val + (1 - lpAlpha) * lpValue;
var lpValue = inputFilter.Process(val);
//hpSignal = hipassAlpha * lpSignal + (1 - hipassAlpha) * hpSignal
// rectify the lpValue again, because the resonance in the filter can cause a tiny bit of ringing and cause the values to go negative again
lpValue = Math.Abs(lpValue);
var mainInput = lpValue;
// 3. Compute the EMA and SMA of the band-filtered signal. Also compute the per-sample dB decay baed on the SMA
var emaValue = ema.Update(mainInput);
var smaValue = sma.Update(mainInput);
// 4. use a latching low-pass classifier to determine if signal strength is generally increasing or decreasing.
// This removes spike from the signal where the SMA may move in the opposite direction for a short period
var movementValue = movementLatch.Update(sma.GetDbDecayPerSample() > 0);
// 5. If the movement is going up, prefer the faster moving EMA signal if it's above the SMA
// If the movement is going down, prefer the faster moving EMA signal if it's below the SMA
// otherwise, use SMA
if (movementValue > 0) // going up
{
combinedFiltered = emaValue > smaValue ? emaValue : smaValue;
}
else // going down
{
combinedFiltered = emaValue < smaValue ? emaValue : smaValue;
}
// 6. use a hold mechanism to store the peak
if (combinedFiltered > hold)
{
hold = combinedFiltered;
lastTriggerCounter = 0;
}
// 7. Choosing the decay speed
// Under normal conditions, use the decay from the SMA, scaled by a fudge factor to make it slightly faster decaying.
// The reason for this is so that we gently bump into the peaks of the signal once in a while.
// If the hold mechanism hasn't been triggered for a specific timeout, then the current hold value is too high, and we need to rapidly decay downwards.
// Use the fastDecay (based on the user- specified release value) as a slew limited value
if (lastTriggerCounter > triggerCounterTimeoutSamples)
{
decay = fastDecay;
}
else
{
decay = Utils.Db2Gain(sma.GetDbDecayPerSample() * 1.2); // 1.2 is fudge factor to make the follower decay slightly faster than actual signal, so we gently bump into the peaks
}
// 7.5 Limit the decay speed in the general range of slowDecay...fastDecay, the slow decay is currently a fixed 3 seconds to -60dB value
if (decay > slowDecay)
{
decay = slowDecay;
}
if (decay < fastDecay)
{
decay = fastDecay;
}
hold = hold * decay;
// 8. Filter the resulting hold signal to retrieve a smooth envelope.
// Currently using 4x 1 pole lowpass, should replace with a proper 4th order butterworth
h1 = holdAlpha * hold + (1 - holdAlpha) * h1;
h2 = holdAlpha * h1 + (1 - holdAlpha) * h2;
h3 = holdAlpha * h2 + (1 - holdAlpha) * h3;
h4 = holdAlpha * h3 + (1 - holdAlpha) * h4;
holdFiltered = h4;
lastTriggerCounter++;
}