Audio disappears in middle of audio track

[JudyArielle]

i am working in a high school classroom that has imac computers that are running on OSX 10.4 operating system.

the problem i am having with audacity is on some of the imacs. the wave will look absolutely normal and produce fine audio and then in the middle of the track the audio cuts out- and in some cases will come back again a little down the waveform. it's as if some of the files in the data folder are missing.

this is especially frustrating for the high school students essentially losing the work they've spent time editing which leads to quite a bit discouragement. i would appreciate any insight you might have to prevent this from happening.

thanks!

[kozikowski]

<<<it's as if some of the files in the data folder are missing.>>>

Backwards. The little files in the _DATA folder are pointing to real audio files that aren't there.

There are no audio files in a Project. To repeat because this is important, when you save a Project, you do not get audio files.

Projects (AUP, AU, _DATA, etc) are traffic cops that point Audacity to the real audio files which are all the original capture or imported sound files. If you delete flute_solo.wav from your hard drive because you're "not needing it any more," you may discover that all the flute parts of your Project vanish. This also happens when people "clean up" their hard drive after editing.

The first two AU files in the _DATA folder are pictures. They're the files that write the blue waveforms on the screen during editing. When you delete the original flute music file, those two pictures get left behind leading to the complaint that "the waveform is still there, but the flute music is gone."

So I would be rooting around in the trash can for those sound files you captured last week during band rehearsal. Anything that can cause Audacity to not find the original music files counts--removing a portable hard drive or USB Dongle, moving music to another folder, etc. Until you Export As Wav... or Export As MP3... (which do give you one single finished sound file), you have no show.

Koz

[JudyArielle]

yes i understand that the original audio is a reference point for audacity files. but what literally happens is that in a single aup audio track- let's say it's a track off of a music cd that had been saved onto the computer in a wav or aiff format- and that came from a single source- that aup file will have audio missing from the middle of it; or perhaps the aup track will begin with a minute of the song and then the rest of the song cannot be heard. these are a couple of examples of this happening.

i am well aware of the fact that the audacity files cannot be renamed or moved until the project has been saved in a wav or aiff file.

[steve]

Just to clarify, is this what you are saying?

You could have a track, 10 minutes long, in Audacity, and it looks fine (all of it).
You start playing the track and it may play the first 2 minutes, but then for the next 2 minutes no sound comes out although it is still playing and everything still looks fine. Then, without doing anything, the sound will come back on again.

If that is what you are saying, and in this example no sound came out from 2 mins to 4 mins, if you then stop Audacity and try playing from 3 minutes into the track, will it play or not?

Also, if you have more than one track of audio, does the sound stop from ALL tracks, or just some of them?

[JudyArielle]

"Just to clarify, is this what you are saying?

You could have a track, 10 minutes long, in Audacity, and it looks fine (all of it).
You start playing the track and it may play the first 2 minutes, but then for the next 2 minutes no sound comes out although it is still playing and everything still looks fine. Then, without doing anything, the sound will come back on again."

Yes this is what i'm saying.

"If that is what you are saying, and in this example no sound came out from 2 mins to 4 mins, if you then stop Audacity and try playing from 3 minutes into the track, will it play or not?"

hmmm.... i'm not sure if i've tried that or not. i think i might have done that just checking out along the track and i feel that it is consistent which part of the track is silent and which part has audio.

"Also, if you have more than one track of audio, does the sound stop from ALL tracks, or just some of them?"

Sometimes it happens on both tracks, but most often it is on just one track. And if it happens on both tracks it is not necessarily at the same time.

[kozikowski]

<<<i am well aware of the fact that the audacity files cannot be renamed or moved until the project has been saved in a wav or aiff file.>>>

Shucks. And I was doing so well, there, too.

<<<Then, without doing anything, the sound will come back on again.>>>

I want you to back up even more and tell me what you were doing to create this show in the first place. Surely somebody must have noticed that as they were creating the show, pieces of it behaved oddly. On the other hand, if the first time somebody noticed a problem was the "dress rehearsal run through" then take the last edit out. A single bad clip can cause edit managers (and the show) to go all nutso--just ask the people over on the Final Cut forum.

Does the damage happen at edit points (as near as you can tell)? Is the damage associated with one clip or sound source? You know how to open each sound clip in QuickTime and Apple-I for info, right? You may find one clip that isn't what you think it is--and it may not be the clip that vanished.

The waveform stayed put and the sound vanished, right?

Since this has happened on more than one machine, can you deduce any pattern there?

Are you listening in Mono--that is, from one speaker? Is it different if you listen on stereo headphones? If there is any question about the stereo-ness of your monitors, you can download the "Left-Right" sound clip from here and try it.

http://www.kozco.com/tech/soundtests.html

Koz

[JudyArielle]

in regards to koz's comments-

yes the waveform stays put (and looks normal) but there is no sound- and no meter indicating that there would be sound during the silent part.
this has happened to students using audacity and we're on break now. so i may need to do some investigative research when we go back in session and then get back with some of the issues you are raising. thanks much for all input.

[kozikowski]

This just reeks of somebody that put a short Music CD passage into the Project and then took the CD out of the machine hours later and didn't connect the two events. "Hey! My Britney Spears clip vanished! How is that possible?"

That's why we need to identify exactly where the clips came from as well as their health.

Koz

[JudyArielle]

i don't think that could be the situation. if the case was that there wasn't the original reference audio available, the entire track would be silent. but parts are heard and then in the same audio track parts are not heard. that is what i don't get about this problem. if it was just that the original reference audio is gone, i would assume that the entire track would be silent?

[kozikowski]

<<<the original reference audio is gone, i would assume that the entire track would be silent?>>>

Yes, that's perfectly correct.

<<<that is what i don't get about this problem.>>>

You're in grand company there.

...and the waveform carries on without sound.......

I'd be interested in what happens if you Export As WAV... and then listen to the result. If the new WAV file goes silent, pay particular attention to what it sounds like at the transition points. Maybe reload it into a fresh Audacity and blow up the transition points. Please note that I got burned by doing this to diagnose a problem. Audacity only builds the waveforms down to -36dB. It flatlines everything below that in the graphic even though the music is still there and perfectly audible.

Close Audacity and open up the clip in QuickTime Player and play it through the "damaged" part.

Do either of these machines exhibit any other oddball symptoms? There is such a thing as a Mac Memory Tester which will exercise the memory modules to try and find a bad one. We're down to the bottom of the pile on this one.

That and I still want to sit in the corner and take notes as you tell us how the problem was discovered. What part of the production process were you on when the problem was discovered. Paint pictures in my head.

Koz