WaveWarp 2.0 Component
      
Spectral Transformers:
Functional Description
Spectral gate
based on direct manipulation of FFT spectra.
All spectral components below a selected magnitude threshold are eliminated.
IMPORTANT: this gating technique is crude but computationally efficient.
It can introduce significant distortion,
depending on the spectral and temporal nature of the audio material being processed.
This can lead to interesting audio effects,
but may be unacceptable for a given application. If accurate gating is required,
refer to the
Dynamic Range Controllers
category of the Component Library.
The attributes of the effect are adjustable via the Parameter Window, as summarised in the
following table. Stereo signals have separate adjustments for left and
right channels.
| Parameter | Purpose |
|---|
| "Threshold" slider |
Adjusts the magnitude threshold. All FFT components below the threshold
are eliminated.
|
| "Buffer length" slider |
Adjusts the length of the input data buffer,
which also defines the "Latency" (overall delay) of the
process.
The FFT buffer size is computed from the "Buffer length"
rounded up to the nearest power of 2
(for efficient FFT computation). If "double zero-padding" is selected, the FFT buffer size is
doubled (after the rounding) to improve the smoothness of the spectrum between successive
FFT bins (but without increasing the underlying frequency resolution).
The input data buffer
is windowed (using a selected profile), then
extended to the length of the FFT buffer by
padding with zeros (on either side). Successive input data buffers are overlapped by a factor
of 2, and the ouputs of the overlapped
inverse transformed buffers are summed, in order
to avoid discontinuities at the window boundaries.
|
| "Output gain" slider |
Adjusts the overall gain of the output signal, after the spectral manipulations have been applied.
|
| "Window type" selection |
Selects the profile of the windowing function applied to the input data.
|
Algorithm
Each successive input buffer
is transformed
to the frequency domain using the windowed-FFT with double overlapping.
The gating is implemented by
eliminating
all FFT components with magnitudes below the selected threshold.
The modified spectrum is then
re-converted to the time domain (using the inverse FFT), and
the overlapped output buffers are summed to yield the output signal.
For an introduction to the Discrete Fourier Transform and the FFT,
see, for example,
[St] sections 4.1 and 4.2.
For further introductory information (with emphasis on audio applications), and
for discussions on spectral measurements, zero-padding,
windowing, the overlap-add re-synthesis method,
and the Short Time Fourier Transform (STFT) for audio applications,
see
[Roa] p. 1084-1112
and
[Moore] p. 61-111.
Signal Implementations
| Audio signals | Control signals | Description |
|---|
| Single input single output mono-mono | n/a | Effect applied to mono input, sent to mono output |
| Single input single output mono-stereo | n/a | Effect applied to mono input with separate settings for left and right stereo output channels |
| Single input single output stereo-mono | n/a | Effect applied with separate settings to left and right stereo input channels, then averaged and sent to mono output |
| Single input single output stereo-stereo | n/a | Effect applied with separate settings to left and right stereo input channels for left and right stereo output channels, respectively |
Related components:
Example DrawingBoards illustrating usage:
|
