Re: silence patch

["Måns Rullgård" <mans@mansr.com>]

fbk-qriry@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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