/// <summary>
/// Construct with configuration and output stream writer
/// </summary>
/// <param name="config"></param>
public Callback(AnalyserConfig config)
{
this.config = config;
// sps is assumed to be even
var sps = config.SamplesPerSlot;
channelData = new Channel[Analyser.CHANNELS];
for (var c = 0; c < Analyser.CHANNELS; c++)
{
channelData[c] = new Channel(config);
}
window0 = new double[sps];
window1 = new double[sps];
window2 = new double[sps];
// Build a triangular window across 3 slots
var half = sps * 3 >> 1;
var end = (sps << 1) - 1;
var step = 1.0 / (half - 1);
for (var i = 0; i < sps; i++)
{
window0[i] = window2[sps - 1 - i] = i * step;
}
for (var i = sps; i < half; i++)
{
window1[i - sps] = window1[end - i] = i * step;
}
}
/// <summary>
/// Generate an audio fingerprint for each selected input audio channel in the buffer
/// </summary>
/// <param name="buffer"></param>
/// <returns></returns>
internal unsafe ulong[] GetAudioFingerprints(IntPtr buffer, AnalyserConfig config)
{
var signatures = new ulong[Analyser.CHANNELS];
// window support
var support = config.SamplesPerSlot * 3;
for (var channel = 0; channel < Analyser.CHANNELS; channel++)
{
var signature = 0UL;
var signalPresent = false;
var cd = channelData[channel];
// Initialise sptr to the first sample for the channel
var sptr = (short *)(buffer) + channel;
var bit = 1UL << config.SlotsPerFrame;
for (var slot = 0; slot < config.SlotsPerFrame; slot++)
{
// Sum of squares of windowed samples
var ssqr = 0.0;
for (var i = 0; i < config.SamplesPerSlot; i++)
{
var sample = *sptr;
// Step to the same channel in the next sample
sptr += Analyser.CHANNELS;
var fsample = cd.Filter.Filter(sample);
cd.Slot2[i] = fsample * fsample;
ssqr += window0[i] * cd.Slot0[i] + window1[i] * cd.Slot1[i] + window2[i] * cd.Slot2[i];
}
signalPresent = signalPresent || (ssqr > 0);
// Convert to logarithmic RMS
// The log scaling ensures that we are working with perceived loudness
var rms = signalPresent ? Math.Log10(ssqr / support) : 0.0;
// Rotate the slot buffers
var tmp = cd.Slot0;
cd.Slot0 = cd.Slot1;
cd.Slot1 = cd.Slot2;
cd.Slot2 = tmp;
bit >>= 1;
var rmsa = cd.RmsBuffer.Average();
if (rms > rmsa)
{
signature |= bit;
}
Buffer.BlockCopy(cd.RmsBuffer, sizeof(double), cd.RmsBuffer, 0, (config.FirLength - 1) * sizeof(double));
cd.RmsBuffer[config.FirLength - 1] = rms;
}
// MSB is a signal present flag
if (signalPresent)
{
signature |= 0x8000000000000000UL;
}
signatures[channel] = signature;
}
return(signatures);
}
public Analyser(AnalyserConfig config)
{
this.config = config;
}