Audio Spectrum CHOP

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Summary
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The Audio Spectrum CHOP calculates and displays the frequency spectrum of the input channels.

In the default Visualization Mode the CHOP is set to display the spectrum in a more understandable way by emphasizing the higher frequency levels and the lower frequency ranges.

In another Mode, the Time to Magnitude and Phase mode, the audio can be converted to the frequency spectrum domain, manipulated and then converted back to get a filtered audio signal. When converting a signal to its spectrum, two channels are created from the one containing the audio signal. One channel contains the magnitude of the frequency components, and the other contains the phase. The channels are named, for example chan1_m and chan1_p where _m and _p are the suffixes for the magnitude and phase channels.

Tip: You can reduce cook time if you decrease the FFT Size from its default 8192 samples. The fastest form of this CHOP is by setting the Output Length parameter to "Output Length Manually". For example set the output buffer size to 2048 samples and the FFT Size to 2048. Each time it cooks, the CHOP is looking at the latest 2028 samples (at 44.1 KHz that amounts to the 50 msec, or 3 frames), which is plenty. Note the default form of the CHOP gives you 22,000 samples: 1 Hz to 22,050 Hz in steps of 1 Hz (when set to Frequency vs Logarithmic scaling), designed for clear interpretation: sample 1000 is the level of audio at 1000 Hz.

See Audio Filter CHOP, Audio Para EQ CHOP, Audio Band EQ CHOP, Audio Oscillator CHOP set to White Noise.

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Parameters - Page

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Parameters - Common Page

Time Slice timeslice - Turning this on forces the channels to be "Time Sliced". A Time Slice is the time between the last cook frame and the current cook frame.

Scope scope - To determine which channels get affected, some CHOPs use a Scope string on the Common page.

Sample Rate Match srselect - - Handle cases where multiple input CHOPs' sample rates are different. When Resampling occurs, the curves are interpolated according to the Interpolation Method Option, or "Linear" if the Interpolate Options are not available.

  • Resample At First Input's Rate first - Use rate of first input to resample others.
  • Resample At Maximum Rate max - Resample to the highest sample rate.
  • Resample At Minimum Rate min - Resample to the lowest sample rate.
  • Error If Rates Differ err - Doesn't accept conflicting sample rates.

Export Method exportmethod - - This will determine how to connect the CHOP channel to the parameter. Refer to the Export article for more information.

  • DAT Table by Index datindex - Uses the docked DAT table and references the channel via the index of the channel in the CHOP.
  • DAT Table by Name datname - Uses the docked DAT table and references the channel via the name of the channel in the CHOP.
  • Channel Name is Path:Parameter autoname - The channel is the full destination of where to export to, such has geo1/transform1:tx.

Export Root autoexportroot - This path points to the root node where all of the paths that exporting by Channel Name is Path:Parameter are relative to.

Export Table exporttable - The DAT used to hold the export information when using the DAT Table Export Methods (See above).


Notes

A reasonable scenario (in terms of CPU usage) is an FFT size of 2048. You get good definition with the spectrum, and also enough padding to (almost) deal with two dropped frames.

An Info CHOP can be attached and the channel hz_per_sample can be viewed. Applicable only of the Frequency axis is set to Linear. With it set to output to normal FFT, to determine the frequency that a given sample represents, use the formula:

In order to convert back to a signal, both channels are required. The suffixes should be the same as those used in the previous Audio Spectrum CHOP.


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