BGC.Audio.Visualization.Spectrogram Class Reference

Static Public Member Functions
static SpectralDecomp	Decompose (IBGCStream stream, int windowCount=400, int windowOrder=12, int targetChannel=0, double minFreq=0.0, double maxFreq=double.PositiveInfinity)

Detailed Description

Definition at line 8 of file Spectrogram.cs.

Member Function Documentation

Decompose()

static SpectralDecomp BGC.Audio.Visualization.Spectrogram.Decompose ( IBGCStream  stream, int  windowCount = 400, int  windowOrder = 12, int  targetChannel = 0, double  minFreq = 0.0, double  maxFreq = double.PositiveInfinity  )

inlinestatic

Definition at line 10 of file Spectrogram.cs.

References BGC.Audio.Visualization.SpectralDecomp.Add(), BGC.Audio.IBGCStream.Channels, BGC.Mathematics.Fourier.Forward(), BGC.Audio.FrequencyDomain.GetComplexSampleFrequency(), BGC.Audio.Envelopes.CosineEnvelope.HammingWindow(), BGC.Audio.Envelopes.IBGCEnvelopeStream.ReadNextSample(), and BGC.Audio.Envelopes.IBGCEnvelopeStream.Reset().

        {
            //WindowSize is 2 ^ windowOrder
            int windowSize = 1 << windowOrder;

            if (stream.Channels <= targetChannel)
            {
                throw new ArgumentException(
                    $"TargetChannel ({targetChannel}) exceeded stream channels ({stream.Channels})",
                    nameof(targetChannel));
            }

            float[] samples = stream.IsolateChannel(targetChannel).Cache().Samples;

            int sampleOffset = (int)((samples.Length - windowSize) / (double)(windowCount - 1));

            //Adjust windowSize to conform to sample size and requirements
            while (sampleOffset <= 0 && windowOrder > 4)
            {
                --windowOrder;
                windowSize = 1 << windowOrder;
                windowCount /= 2;
                sampleOffset = (int)((samples.Length - windowSize) / (double)(windowCount - 1));
            }

            if (windowOrder == 4)
            {
                throw new ArgumentException("Clip too short to evaluate");
            }

            if (maxFreq == double.PositiveInfinity)
            {
                //Default MaxFrequency to be determined by the size of the window
                maxFreq = FrequencyDomain.GetComplexSampleFrequency(windowSize, windowSize / 2);
            }

            //Limit Max Frquency by the size of the window
            maxFreq = Math.Min(maxFreq, FrequencyDomain.GetComplexSampleFrequency(windowSize, windowSize / 2));

            //Limit Min Frequency by the 
            minFreq = Math.Max(minFreq, FrequencyDomain.GetComplexSampleFrequency(windowSize, 1));

            //Our output will be just the real-valued amplitudes
            SpectralDecomp decomp = new SpectralDecomp(minFreq, maxFreq, windowSize, windowCount);

            Complex64[] fftBuffer = new Complex64[windowSize];

            IBGCEnvelopeStream hammingWindow = new EnvelopeConcatenator(
                CosineEnvelope.HammingWindow(windowSize / 2, true),
                CosineEnvelope.HammingWindow(windowSize / 2, false));

            for (int window = 0; window < windowCount; window++)
            {
                int specificOffset = sampleOffset * window;
                hammingWindow.Reset();

                //Copy samples into buffer
                for (int i = 0; i < windowSize; i++)
                {
                    //Set real value
                    fftBuffer[i] = samples[specificOffset + i] * hammingWindow.ReadNextSample();
                }

                Fourier.Forward(fftBuffer);

                decomp.Add(window, fftBuffer);
            }

            return decomp;
        }

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The documentation for this class was generated from the following file:

• Audio/Spectrogram/Spectrogram.cs