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5b3388e4ac
Add an option to do a hilbert transform on the generated rear channels to do a 90 degree pahse shift on them. This can improve spacialization of the rear channels. See #861
69 lines
1.9 KiB
C
69 lines
1.9 KiB
C
/* Hilbert function
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*
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* Copyright © 2021 Wim Taymans
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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*/
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#ifndef HILBERT_H
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#define HILBERT_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <errno.h>
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#include <stddef.h>
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#include <math.h>
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static inline void blackman_window(float *taps, int n_taps)
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{
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int n;
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for (n = 0; n < n_taps; n++) {
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float w = 2 * M_PI * n / (n_taps-1);
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taps[n] = 0.3635819 - 0.4891775 * cos(w)
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+ 0.1365995 * cos(2 * w) - 0.0106411 * cos(3 * w);
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}
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}
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static inline int hilbert_generate(float *taps, int n_taps)
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{
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int i;
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if ((n_taps & 1) == 0)
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return -EINVAL;
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for (i = 0; i < n_taps; i++) {
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int k = -(n_taps / 2) + i;
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if (k & 1) {
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float pk = M_PI * k;
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taps[i] *= (1.0f - cosf(pk)) / pk;
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} else {
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taps[i] = 0.0f;
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}
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}
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return 0;
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}
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#ifdef __cplusplus
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} /* extern "C" */
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#endif
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#endif /* HILBERT_H */
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