MP3 conversion glitches

Paul-Fegan wrote on 8/8/2025, 9:03 AM

I've been using various version of SF to convert to MP3 for years without issue. Usually, I was batch converting files for elearning to 128 kbps MP3s. But recently, I had to batch convert some WAVs for an audiobook. The WAVs all meet the ACX specifications (as tested in SF18), but this time, I need to convert to 192 kbps. The problem is that it's introducing random audio glitches. You could batch the same file twice and the glitches wouldn't necessarily be in the same place. Has anyone else encountered this? I could export to a higher bitrate like 320, but Audible says it's unnecessary and I'd rather just meet the spec. I'll do it, though, if the files are glitch free and I've no other option.

So does anyone know if conversion from 44 kHz, 16 bit, mono WAV to 192 kbps MP3 should cause a problem?

Many thanks.

Comments

SP. wrote on 8/8/2025, 9:22 AM

@Paul-Fegan If you open the Sound Forge program preferences while holding the SHIFT key, there will be an additional Internal tab available. There you should be able to activate the legacy MP3 encoder. This one might work better.

Paul-Fegan wrote on 8/8/2025, 9:25 AM

Oh cool. Thanks, SP. I shall give that a go. I notice in older version of SF (13 and earlier), it would only allow a bitrate of 128 kbps if your file was mono, which audiobook files tend to be. I'll see if this is the case when I try the legacy encoder. Thanks again.

rraud wrote on 8/8/2025, 9:37 AM

does anyone know if conversion from 44 kHz, 16 bit, mono WAV to 192 kbps MP3 should cause a problem?

Hi @Paul-Fegan, what version of SF are you using?
The later versions of Sound Forge has a (hidden) option to use the legacy MP3 encoder or the 'newer' (default) encoder which some parameters like 'joint stereo' cannot be disabled... though I have not experienced any encoding issues regardless if the source file is mono or stereo and/or is encoded in mono or stereo. I would recommend single-channel mono for spoken word projects since there is typically no spacial (stereo) information like music or S/FX, Plus encoding a mono MP3 will double the resolution at the same bitrate and file size as stereo and still meets ACX specs.

Paul-Fegan wrote on 8/8/2025, 9:49 AM

Hi Rick, I'm using SF18, but am trying this in SF14 now, too. I've just encoded one chapter on its own in SF14 and so far, it seems OK. But it's so random that one file could be fine and another might have glitches. And yes, as mentioned, I'm converting a 44 kHz, 16 bit, mono file as it's just voice, so no stereo files are involved.

I'll convert another file in SF14 and if it works OK, I'll try them all. If it fails, I'll try the legacy encoder you and SP mentioned. Thanks a mill.