MzSpectrogramClient

SYNOPSIS

MzSpectrogramClient -- Demonstration of how to create spectral data from time data supplied by a host application.

The MzSpectrogramClient plugin accepts time-sequence audio data as input from the host application and applies a Fourier transform to the data generate a spectrum. The plugin then calculates and outputs the non-negative frequency magnitude spectrum.

MzSpectrogramClient generates 1 output:

1.

The MzSpectrogramClient plugin produces the same output as the MzSpectrogramHost plugin. The difference between the two plugins is how the output is produced. MzSpectrogramHost receives the pre-calculated complex frequency spectrum from the host, while MzSpectrogramClient receives the time-based audio signal from the host and then calculates the complex frequency spectrum itself.

The MzSpectogramClient is a useful template for how to write your own frequency analysis plugin where more control over the transform process is necessary, or you want to implement a transform other than a Discrete Fourier Transform, such as a wavelet transform. Also, the analysis window applied to the audio signal in MzSpectrogramHost is controlled by the host (usually selected by the user, or set to a default type). If your plugin needs a specific analysis window which cannot be supplied by the host, then you should use a client-based transform as given in this example plugin. While MzSpectrogramHost just calculates the magnitude spectrum directly from the complex spectrum data sent by the host, MzSpectrogramClient requires three prepatory steps to generate the spectrum in the process() function:

1. Generate an analysis window (done once for all processing in the initialise() function)
2. Apply the analysis window on the input signal
3. Apply the Fast Fourier Transform to the signal

Notice that the parameter list of the makeMagnitudeSpectrum() function had to be changed from the one in MzSpectrogramHost because the output of the fft() function does not interleave the real and imaginary components of the complex spectrum.

Also notice that the function getInputDomain returns the value TimeDomain rather than FrequencyDomain since the client plugin receives time data and will calculate its own frequency domain data.

Compiled versions of the MzSpectrogramClient plugin can be downloaded from the download page.

The source code for the plugin was last modified on 23 Jun 2006.

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In order of complexity:
1. MzSpectrogramHost -- demonstrates how to receive and process spectral data from the host application.
2. MzSpectrogramClient -- described on this page: demonstrates how to generate and process spectral data generated from time data provided by the host application.
3. MzSpectrogramFFTW -- demonstrates how to do three-to-four times faster Fourier transforms than MzSpectrgramClient.
4. MzNevermore -- a full-featured Spectrogram display function based on MzSpectrgramFFTW.