MP3 Puzzle

[dlowerre]

I am trying to import an mp3 that can be found at this address:

http://vocalharmonies.com/music/tags/tag-001.zip

The track I am having trouble with is tag-001-bs.mp3

When I try to open or import this track, the beginning of the track is chopped off. When I play the mp3 with Totem (yes I am on linux) the whole track plays.

Could this track be protected in some way?

[steve]

It's not protected, but it is slightly malformed.

If you use VLC to convert it to WAV, then you will able to edit the WAV in Audacity.

(The first thing you will probably want to do is to sort out the huge amount of DC offset - run it through a high-pass filter set to a very low frequency, say around 20Hz).

[dlowerre]

Thanks again! You are a wonder.

I am ignorant of some basic understanding here and if you are so inclined perhaps you could enlighten me:

Why does putting the track through a high-pass filter with a low cutoff remove the dc offset? It does, obviously but I dont understand why? Is it a by-product of the equalization? I had previously used the 'remove dc offset' feature of the normalize algorithm but it merely shifts the signal or so it seems, so it was useless on this sample.

Also, despite its offset it sounded ok to me before I processed it. I even tried comparing the original to the bandpassed simultaneously by panning one right and one left. I just cant hear any difference. What is it that is gained by removing the dc offset in this circumstance?

If you are busy helping others as you have helped me then I can live without an answer. I have noticed that you are exceedingly active on this forum.

[kozikowski]

<<<If you are busy helping others as you have helped me then I can live without an answer.>>>

The others can wait.

DC, Direct Current, or plain battery voltage is not sound, but sometimes gets mixed into a sound performance when there is a bad adjustment somewhere or an actual defective electronic component (or sometimes just a cheap sound card). Since battery voltage does not produce a vibration in the air, you can't hear it, but it makes editing, cutting, filtering, and managing the performance extremely difficult. So we get rid of it.

You can do that filter trick, but Audacity already has a tool that does this. Effect > Utility > DC Bias Removal. In earlier Audacity versions, it was buried inside the Effect > Normalize tool. This prepared tool removes the battery voltage from your performance without affecting the sound in any way.

Koz

[dlowerre]

Thanks, Koz! Very clear, and concise!

[John Sprung]

<<<If you are busy helping others as you have helped me then I can live without an answer.>>>
Since battery voltage does not produce a vibration in the air, you can't hear it, but it makes editing, cutting, filtering, and managing the performance extremely difficult. So we get rid of it.

Interesting -- Perhaps that fix should be a default whenever an MP3 is opened. If for some reason you really needed to see the DC, you'd have to uncheck a box first.




-- J.S.

[kozikowski]

<<<Perhaps that fix should be a default >>>

Don't start that. I don't think Audacity should ever have DC in it at all since battery voltage is not and never has been "sound."

The developers want to take whatever is there because filtering it out takes time -- sometimes lots of time.

I capture stuff on line all the time and have to stop and take the DC out. It's a lot more common than everybody thinks. I put a microphone to USB converter in the garage (next to the iMic) because of excessive battery voltage leaking into the show.

Koz