fbk-qr...@zacglen.net writes:
> There is a bug in the "silence" effect that appears to
> have been introduced in 2009 with commit bbb403.
>
> In function aboveThreshold() the value being scaled
> is effectively the result of a sqrt but when it
> gets scaled the value is not rounded but coarsely truncated instead.
> Truncation is wrong. Rounding is right.
>
> Prior to this commit the value was effectively
> rounded to the nearest whole value (according to
> the precision). Without the following patch the "silence"
> results are considerably different to earlier versions.
>
> For example:
>
> value old masked current
> ----- ---------- -------
> 0x009bd6ae 0x0000009c 0x009b0000
> 0x00a170b8 0x000000a1 0x00a10000
>
> The 0x009bd6ae used to be correctly rounded to 0x9c whereas
> the current version effectively truncates the value to 0x9b.
>
> That is a serious flaw that should have been picked up
> during testing. But better discovered 11 years later by a
> random member of the public than never.
The only serious flaw I see here is your condescending tone.
> The patch:
>
> ======================================================================
> --- sox-downstream-sox-14.4.2.0.modified/src/silence.c.jw
> +++ sox-downstream-sox-14.4.2.0.modified/src/silence.c
> @@ -277,9 +277,15 @@
> {
> /* When scaling low bit data, noise values got scaled way up */
> /* Only consider the original bits when looking for silence */
> - sox_sample_t masked_value = value & (-1 << (32 -
> effp->in_signal.precision));
> + double scaled_value;
> + sox_sample_t rounded_value = value;
>
> - double scaled_value = (double)masked_value / SOX_SAMPLE_MAX;
> + /* before we mask we should round the value */
> + if (effp->in_signal.precision < 32)
> + rounded_value += (1 << (32 - effp->in_signal.precision - 1));
> + rounded_value &= (-1 << (32 - effp->in_signal.precision));
> +
> + scaled_value = (double)rounded_value / SOX_SAMPLE_MAX;
>
> if (unit == '%')
> scaled_value *= 100;
> ======================================================================
>
> :JW
>
--
Måns Rullgård
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