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doc: clarify the dither.noise

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Fixes #4057
This commit is contained in:
Wim Taymans 2024-06-13 11:38:26 +02:00
parent 0115042adb
commit b421331275
2 changed files with 26 additions and 4 deletions
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8
spa/plugins/audioconvert/fmt-ops.c
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@ -468,6 +468,8 @@ int convert_init(struct convert *conv)
const struct noise_info *ninfo;
uint32_t i, conv_flags, data_size[3];
/* we generate int32 bits of random values. With this scale
* factor, we bring this in the [-1.0, 1.0] range */
conv->scale = 1.0f / (float)(INT32_MAX);
/* disable dither if not needed */
@ -483,6 +485,9 @@ int convert_init(struct convert *conv)
switch (conv->noise_method) {
case NOISE_METHOD_NONE:
conv->noise_method = NOISE_METHOD_PATTERN;
/* the pattern method does not use a random number
* but flips the noise between [-(1<<(N-1)), 0] every
* 1024 samples. */
conv->scale = -1.0f * (1 << (conv->noise_bits-1));
break;
case NOISE_METHOD_RECTANGULAR:
@ -490,10 +495,13 @@ int convert_init(struct convert *conv)
SPA_FALLTHROUGH;
case NOISE_METHOD_TRIANGULAR:
case NOISE_METHOD_TRIANGULAR_HF:
/* Amplify the random noise, with additional
* N-1 bits of noise. */
conv->scale *= (1 << (conv->noise_bits-1));
break;
}
}
/* RECTANGULAR dither goes from [-0.5, 0.5] */
if (conv->noise_method < NOISE_METHOD_TRIANGULAR)
conv->scale *= 0.5f;