Re: Question about ABR Presets on CBR mode

Thanks for the reply.
​
I'm afraid I need to preserve original loudness as possible while encoding them at low bitrates,
and 0.45 LUFS means much.
​
And the audio is silent enough that no clipping would occur.
​
Is there any frontend option that effectively disable volume scaling?
​
I found that '--scale 1.05263' works, but... you know :)
​
Best Regards,
Jang Ryeol

-----Original Message-----
From: "Gabriel Bouvigne"<[email protected]>
To: "장렬"<[email protected]>;
Cc: <[email protected]>;
Sent: 2019-06-19 (수) 19:02:25 (GMT+09:00)
Subject: Re: [Lame-dev] Question about ABR Presets on CBR mode
 
On 2019-06-19 07:01, 장렬 wrote:
> I noticed ABR presets applied when CBR is on.
> ​
> A side effect of this is decreasing loudness on low bitrates(~192kbps).
> ​
> /* ABR seems to have big problems with clipping, especially at low
> bitrates */
> /* so we compensate for that here by using a scale value depending on
> bitrate */
> lame_set_scale(gfp, lame_get_scale(gfp) * abr_switch_map[r].scale);
> ​
> ------------------------------------
> ​
> Is this a bug, or a feature? Is apply_abr_preset necessary for CBR?


Hello,

It's actually a feature. Clipping after encoding/decoding is more likely
to happen at lower bitrates, and this is actually applicable to both CBR
and ABR. What causes clipping is the rounding/changing of values due to
requantization, which is coarser when the bitrate is lower.

Regards,

--
Gabriel Bouvigne


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