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Question (or Task)

I want to extract a single resynth track from a live spectral analysis. Is there a way to avoid the jitter caused by the frequency shift?

I tried with "all" possible settings in LiveSpectralAnalysis module without success. I think a kind of a Slew rate limiter or a hysteresis parameter built-in the LiveSpectralAnalysis module would work.

-- KarlMousseau - 24 Feb 2004

Solution(s)

You could use the SpectrumTrackSelector to obtain the amplitude and frequency envelopes of a specific track. Once you have that signal, you could use any of these modules to smooth the envelopes: AmplitudeFollower, PeakDetector, AveragingLowPassFilter, LowpassFilter. After smoothing, you could use the envelopes to control the amplitude and frequency of a single Oscillator.

-- KurtHebel - 24 Feb 2004

It seems that SpectrumTrackSelector outputs mono only. Is it possible to "split" its output to get separate amp and freq tracks?

I understand I should use AmpFollower etc... but I don't understand how a LowPassFilter could help.

-- KarlMousseau - 25 Feb 2004

From the SpectrumTrackSelector on line description: Extracts a single amplitude envelope and frequency envelope from the Spectrum input. The amplitude envelope will appear at the left output, and the frequency envelope will appear at the right. To extract the amplitude envelope ONLY, check the Amp box and uncheck the Freq box. Typically the output of the SpectrumTrackSelector is used to control a parameter of another Sound.

You can either use two SpectrumTrackSelectors (one for the amplitude envelope and one for the frequency envelope) or you can use a single SpectrumTrackSelector and run it through a LeftChannelOnly and a RightChannelOnly to obtain separate envelopes.

Sudden changes or jumps in the envelope's value correspond to high frequencies (just like sharp edges or jumps in an audio signal). If we filter the envelope signal with a low pass filter, the filter will remove the high frequency components (if the cutoff frequency is low enough), smoothing out the sudden changes and jumps.

The only trick is relating cutoff frequencies to smoothing times. Since time and frequency are related, you can use something like 100 ms hz in the Cutoff field of a LowPassFilter to smooth the envelope with an approximate 100 ms time constant.

-- KurtHebel - 25 Feb 2004

I was misleaded by the single line output of the SpectrumTrackSelector ... It is slowly getting there. Still, how do I convert SpectrumTrackSelector Freq output into hertz (to control single oscillator pitch). I put a SoundToGlobalController after the SpectrumTrackSelector to monitor its output; at first glance, it appears that the range 0-1 corresponds to 0 hz to half samplerate. Is SpectrumTrackSelector L * SignalProcessor halfSampleRate right?

-- KarlMousseau - 26 Feb 2004

Yes, the frequency envelope is in the range of 0 to 1 which corresponds to 0 to the half sample rate when the spectral source is linear. Linear spectral sources are the LiveSpectralAnalysis and the SpectrumFromArray (with Log unchecked). The SpectrumFromRAM module outputs a log spectrum, so you need to route its output through a SpectrumLogToLinear module before using it.

-- KurtHebel - 26 Feb 2004