From b4ad13420f57ff7b2a411f2f70217635d1516a80 Mon Sep 17 00:00:00 2001 From: Jason Jang Date: Fri, 28 Jan 2022 17:08:27 -0800 Subject: [PATCH] avfilter/af_apsyclip: fix FFT bin indexing With a complex FFT instead of real FFT, the negative frequencies are not dropped from the spectrum output, so they need to be scaled when the positive frequencies are scaled. The location of the top bin is also different. Signed-off-by: Jason Jang --- libavfilter/af_apsyclip.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) diff --git a/libavfilter/af_apsyclip.c b/libavfilter/af_apsyclip.c index dc3a8e97e4..0bc469c1a1 100644 --- a/libavfilter/af_apsyclip.c +++ b/libavfilter/af_apsyclip.c @@ -292,10 +292,9 @@ static void calculate_mask_curve(AudioPsyClipContext *s, if (i == 0) { magnitude = FFABS(spectrum[0]); } else if (i == s->fft_size / 2) { - magnitude = FFABS(spectrum[1]); + magnitude = FFABS(spectrum[s->fft_size]); } else { - // although the negative frequencies are omitted because they are redundant, - // the magnitude of the positive frequencies are not doubled. + // Because the input signal is real, the + and - frequencies are redundant. // Multiply the magnitude by 2 to simulate adding up the + and - frequencies. magnitude = hypotf(spectrum[2 * i], spectrum[2 * i + 1]) * 2; } @@ -315,10 +314,9 @@ static void calculate_mask_curve(AudioPsyClipContext *s, for (int i = s->num_psy_bins; i < s->fft_size / 2 + 1; i++) { float magnitude; if (i == s->fft_size / 2) { - magnitude = FFABS(spectrum[1]); + magnitude = FFABS(spectrum[s->fft_size]); } else { - // although the negative frequencies are omitted because they are redundant, - // the magnitude of the positive frequencies are not doubled. + // Because the input signal is real, the + and - frequencies are redundant. // Multiply the magnitude by 2 to simulate adding up the + and - frequencies. magnitude = hypotf(spectrum[2 * i], spectrum[2 * i + 1]) * 2; } @@ -360,19 +358,20 @@ static void limit_clip_spectrum(AudioPsyClipContext *s, for (int i = 1; i < s->fft_size / 2; i++) { float real = clip_spectrum[i * 2]; float imag = clip_spectrum[i * 2 + 1]; - // although the negative frequencies are omitted because they are redundant, - // the magnitude of the positive frequencies are not doubled. + // Because the input signal is real, the + and - frequencies are redundant. // Multiply the magnitude by 2 to simulate adding up the + and - frequencies. relative_distortion_level = hypotf(real, imag) * 2 / mask_curve[i]; if (relative_distortion_level > 1.0) { clip_spectrum[i * 2] /= relative_distortion_level; clip_spectrum[i * 2 + 1] /= relative_distortion_level; + clip_spectrum[s->fft_size * 2 - i * 2] /= relative_distortion_level; + clip_spectrum[s->fft_size * 2 - i * 2 + 1] /= relative_distortion_level; } } // bin N/2 - relative_distortion_level = FFABS(clip_spectrum[1]) / mask_curve[s->fft_size / 2]; + relative_distortion_level = FFABS(clip_spectrum[s->fft_size]) / mask_curve[s->fft_size / 2]; if (relative_distortion_level > 1.f) - clip_spectrum[1] /= relative_distortion_level; + clip_spectrum[s->fft_size] /= relative_distortion_level; } static void r2c(float *buffer, int size)