- SoundHack Spectral Shapers
Many readers of this journal will be familiar with Tom Erbe's signal processing software, particularly Sound Hack, which for years has been a staple soundfile processing tool for the Macintosh platform. These new Spectral Shapers implement some of the functionality of SoundHack in popular plug-in formats and for real-time use.
SoundHack, for the uninitiated, is a soundfile processor that implements many of the computer music community's most esoteric processing techniques, such as convolution and cross-synthesis, in a way that most musicians can use. SoundHack has had some 15 years of development and implementation, and as it has concentrated on techniques which commercial software avoids it has very few competitors. The suite of four new real-time plug-ins now on offer implements some of Sound Hack's simpler functions, and one function not found in SoundHack. As computer processing ability increases, Mr. Erbe intends to release more real-time plug-ins based on SoundHack functionality.
The SoundHack Spectral Shaper plug-ins come in the popular VST format for Macintosh OS 9, Mac OS X and Windows computers; they also come in Audio Units format for Mac OS X. As the bundle name suggests, each of the four plug-ins implements filters for spectral or timbre modification and shaping. +Spectralcompand is a spectral compressor and expander, +Spectralgate is a spectrum-based noise gate, +Binaural is an HRTF (Head Related Transfer Function) filter for positioning sounds at specific locations around the listener's head, and +Morphfilter holds two filter shapes and allows the user to transform one filter to another.
Installation is trivial: simply unpack the archive and place the plug-ins in the correct folder on your computer. This varies from one operating system to another and clear and accurate instructions are given in the documentation. Important to note for Windows users is that the plug-ins require Apple's QuickTime 5 (or later) to be installed. The plug-ins can be used for 14 days without registering them. Registration requires the use of a small utility program, Spectral Shapers Unlock, to enter the user's name and registration code.
Upon opening any of the plug-ins one cannot help but notice the unique user interface (see Figures 1–4), in colors reminiscent of the original iMacs. A graphical area displaying spectrum information dominates each plug-in interface and on +Binaural this space is shared by a low frequency oscillator (LFO) envelope editor. The interface includes a peak program meter display on the right side displaying the output level from the plug-in, and below the graphical display are a number of rotary "knob" controls to adjust the parameters of the filters. There are also a [End Page 105] number of toggle buttons between the large graphical display area and the knobs to select such parameters as linear or logarithmic display, stereo linking, resetting controls, and so on. The graphical display shows the input spectrum and the output spectrum, along with the filter shaping function, all updated in real-time.
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+Spectralgate (see Figure 1) is a frequency-selective, or spectral, version of the familiar noise-gate/ducker. This plug-in separates the spectrum into 513 bands and uses a threshold parameter to affect the sound in frequency bands either above or below the threshold only. The gate function will eliminate frequency bands below the threshold while the "ducking" function reduces the level of frequency bands above the threshold. The ducking gain reduction is less severe than the gate function. Thus the dynamic level of each band is changed depending on its level. Ducking will work on louder spectral bands, higher than the threshold (a resonance for example), to reduce their level, while gating affects frequency bands below the threshold. +Spectralgate can thus be used to only allow louder frequency bands through, as timbral modification or possibly...