K404/K504 Assignment 3: SoundHack and Spear

SoundHack

SoundHack is a program that lets you perform various sound processing techniques that might not be available (at least with the same degree of flexibility) in commercial programs like Digital Performer and Pro Tools. SoundHack also lets you convert from one sound file format to another.
  1. Open a sound file in SoundHack. Choose the Hack > Phase Vocoder menu command.

    Set Bands to the number of FFT bands you want to use. A large number of bands yields better frequency resolution, while a small number of bands yields better time resolution. The Window popup menu allows you to choose different pre-FFT windows for different filtering characteristics. Hamming, von Hann, and Kaiser windows.

    The Overlap setting adjusts the size of the FFT window, relative to the number of FFT bands, for analysis and synthesis. A large setting (4x) differentiates better between frequencies that are between bands but responds to amplitude changes more slowly.

    Click the Time Scale button for time scaling, or the Pitch Scale for pitch scaling. Enter the scale factor next to the Scaling popup menu (above the Pitch Scale button). This popup menu lets you enter desired length (for time scaling) or semitone transposition (for pitch scaling).

    If you want the time or pitch scaling factor to change during processing, click the Scaling Function check box, and then Edit Function. This brings up the Function Window editor, in which you can draw a time-varying scaling function.

  2. Open a sound file in SoundHack. Choose Hack > Convolution. Click the Pick Impulse to select a different impulse sound file.

    Click Process to write the convolution result to a file. The success of the sound depends on the spectral characteristics of the source and impulse sound files. If you have an impulse response file that captures the reverberation characteristics of a hall (for example, these files, then you can apply those reverb characteristics to the source sound. (This is how convolution reverb effects work.) But this isn't the only way to use convolution. Experiment! Usually, things work best if one of the files has a lot of broadband energy.

For more help with SoundHack, see the online manual.

Spear

The Spear program is a very interesting FFT-based spectral processor. It lets you visualize and manipulate the independent FFT bands.

  1. Open a sound file in Spear program. (Just press the Analyze button in the dialog that appears.) You can play and stop the sound by toggling the space bar.
  2. Experiment with the Controls window to change pitch, speed, etc.
  3. Use the Lasso Selection tool to select part of the spectrum. You can play only this part by holding down the shift key while pressing the space bar.
  4. Then use the tools in the palette, or the commands in the Transform menu to manipulate the selected part of the spectrum.

  5. Save the results to a new sound file. No, you don't do this by using the File > Save command. That saves a spectral analysis file in the SDIF format. Instead, use Sound > Synthesize to File.

©2008, John Gibson, Christopher Cook