WaveWarp 2.0 Component
      
Spectral Transformers:
Functional Description
Spectral cross-synthesis
based on direct manipulation of FFT spectra.
The audio output is derived from a
"blend" of the input audio spectra.
Specifically, the phase of the first input spectrum
is combined with the magnitude of the second.
The characteristics of the
spectral
cross-synthesis are adjustable via the Parameter Window, as summarised in the
following table.
| Parameter | Purpose |
|---|
| "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.
|
| "Blend factor" slider |
Adjusts the extent of the spectral blending.
|
| "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 spectra of the two input signals are blended on a point-by-point basis
by combining the phase of the first input
with the magnitude of the second.
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 stereo-mono | n/a | Left input blended with right input, sent to mono output |
| Single input single output stereo-stereo | n/a | Left input blended with right input, sent (in duplicate) to stereo output |
| Double input single output mono-mono | n/a | First mono input blended with second mono input, sent to mono output |
| Double input single output mono-stereo | n/a | First mono input blended with second mono input, sent (in duplicate) to stereo output |
| Double input single output stereo-mono | n/a | Average of left and right channels of first input blended with average of left and right channels of second input, sent to mono output |
| Double input single output stereo-stereo | n/a | Average of left and right channels of first input blended with average of left and right channels of second input, sent (in duplicate) to stereo output |
Related components:
Example DrawingBoards illustrating usage:
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