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Topic: MP3 decoded with SoundForge (Read 4249 times) previous topic - next topic
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MP3 decoded with SoundForge

Hello.

Just registered at the forum because I stumbled onto a perplexing issue.    I got an MP3 song with a pop at the end so I wanted to convert the MP3 to WAV, edit it in SoundForge 4.5 (which happens to be my favourite WAV editor) and then re-compress it with LAME.

I normally convert MP3 to WAV with LAME.exe itself (using Lame-Front-End), which I did, and then loaded it into SoundForge. Then, by chance, I decided to simply drag the MP3 into SoundForge, and I noticed that the pop at the end of the song was different between the loaded WAV file and dragged-in MP3 file (which had a louder pop).

Now I'm confused. I've been working with WAVs, MP3s and SoundForge for years and I never noticed that. Shouldn't both waveforms be identical once loaded into SF ? As far as I understand it, dragging the MP3 into SF basically converts it to WAV in the background and displays the waveform. And shouldn't a decoded MP3 produce exactlly the same WAV file in any decoder ?

I also tried converting the MP3 to WAV using "freac" and the result was identical to the WAV that LAME.exe produced. I then dragged the MP3 into a newer SoundForge Pro 10, and that one again produced a different waveform, just like the older SF 4.5.

If the sound of the pop is different then I'm guessing the whole song could sound different, all depending on whether I drag the MP3 directly into SF or whether I decode it to WAV beforehand. I have no idea why SoudForge(s) produce a different waveform than LAME or freac.

Any ideas what is happening here ?

Thanks.

MP3 decoded with SoundForge

Reply #1 –
It's my understanding that there is a "reference decoder" (somewhere) and the decoding should be the same.    Encoding can be different.

If the pop is at the absolute end (maybe a DC offset problem?) maybe  it's just an end-point problem and the file is otherwise the same...

Quote
so I wanted to convert the MP3 to WAV, edit it in SoundForge 4.5 (which happens to be my favourite WAV editor) and then re-compress it with LAME.
MP3DirectCut can do limited editing, such as trimming, muting, or fading without decompressing and then going through a 2nd lossy compression step.  And, it should save some time once you get familiar with it.

MP3 decoded with SoundForge

Reply #2 –
If the file has a corrupted frame that doesn't decode properly, different decoders might handle it better or worse.