Single file with wrong Tempo, wrong volume, no waveform

Audacity Help Forum Windows
1

Greetings everyone,

I spent several hours looking for an answer to this issue in various parts of the internet as well as this forum, and while I found a few issues that were somewhat similar, I wasn’t able to locate anything relating to my specific problem.

I’ve been using Audacity 2.0.5 for about a month now and I think its amazing software. It’s been working absolutely fine for me ever since I began with it, but, while recording an audio segment for a video project this past Saturday using a conventional microphone, I found one of the files horribly distorted. The first clue that something was wrong was that the waveform in the topmost track was missing. (This has actually happened before, but I thought very little of it because usually the audio still works and if I truly need the waveform exporting the file out and back in as an MP3 usually brings it up) When I tried to playback the audio, it was extremely quiet, I had to Amplify it up to 40 dB to be able to hear it at a normal level, (at which point the waveform appears) but when I am able to hear it, the tempo was drastically increased. (By about 40% the piece that was supposed to be 52 minutes long is currently 31 minutes) I was able to fix the tempo with the Change Tempo effect, but now the audio sounds very echo-y, like I recorded it in a fish tank. I recorded two other pieces of audio that night after this one and they both work fine, its only this single, solitary file I’ve ever had an issue with. I had a USB webcam recording simultaneously with audacity, and the audio from the webcam doesn’t have this problem. (It just sounds like garbage, cuz, ya know, webcam) From my research this seems to be indicative of an issue with the sound card, but, to be frank, I don’t have one. The computer I record on is a workstation that runs on integrated audio, and furthermore, if it was a hardware issue, why would it work perfectly for a month, screw up once, and then go right back to working perfectly?

The audio on that file represents a very important segment I am loathe to lose. Can anything be done to salvage it? And are there any steps I can take to ensure this doesn’t happen again?

Thank you for your time.

Using:
Windows 7 Professional 64 Bit (2 GB RAM)
Pyle PDMIKC Professional Conference Microphone
Microsoft LifeCam VX-3000

2

That microphone is a “broadcast” type with a male XLR3 connector to plug into a mixer or other system. It seems like a very nice microphone. It also has a 9 volt power supply of some sort. What’s the possibility of a damaged supply or a bad connection? Is the supply hanging half-way out of the socket? Is a chair leaning on it? Is the connection to the microphone secure?

tempo was increased

That’s the phrase that pays. A performance that is too fast was recorded too slow. The computer could not keep up with the process and it started to drop tiny pieces here and there. In extreme, there can actually be silent patches where the computer threw up its little hands and quit for a while. That in addition to the extreme low volume tells me the recording system was in significant distress during that performance.

Patching it together the way you’re doing it is about all we can do. 40dB is an extreme about of volume boost for a recording. Another 20dB or so quieter than that and you’re at the dead bottom noise floor of a lot of equipment. As low as it goes. So for that one recording, the normal volume management and digital encoding shut down.

Koz

3

Zero. Like I said, I did two other recordings that night, roughly the same length, all three with about a 15 minute break in between, without the computer itself being touched, and the other two were fine. The mic sat in the middle of the table unobstructed and untouched.

The only things that were running on the computer was Audacity and Windows Movie Maker. (for the webcam recording) If such is the case, why was the webcam audio not similarly affected?

4

I don’t know. I’m only telling you what the key words mean. Speeded up shows almost always means the computer was recording too slow for some reason. When people complain about a slow show that’s more difficult. That’s a different error and much more unusual, but speeded up is a common red flag.

What do you know about the workstation’s tasks? Do you have it set to do auto Windows updates? I refuse to let any of my machines do auto anything.

I had a machine produce a seriously scrambled performance as if it was trying to jam two different recordings of the same show in the same track. It never did that before and it hasn’t happened since.

Programmers call that “Moon Phase” errors.

Koz

5

I can’t help asking if you watch the Audacity red recording meters when you capture a show?

It’s pretty common to press record and hope to goodness that Audacity is doing its job. I’m betting you didn’t get meters during that session. You said you didn’t get the blue waves.

The first clue that something was wrong was that the waveform in the topmost track was missing. (This has actually happened before, but I thought very little of it because usually the audio still works and if I truly need the waveform exporting the file out and back in as an MP3 usually brings it up)

So you have a known problem with this machine and it appears to be getting worse. No, it’s not normal for either the blue waves or the sound meters to be missing during a recording.

Koz

6

the waveform in the topmost track was missing.

The topmost track of how many? If you’re overdubbing, there’s a limit to the number of tracks that Audacity can simultaneously manage. Koz

7

You’re absolutely right, I never thought to check for meters. And to be honest I never noticed if the blue waves were missing during recording or just when I played it back. I always assumed the latter, but I’ll be sure to check for them next time as well.

And yes, the workstation is set to auto-update. Would you recommend disabling them, then?

I do sincerely thank you very much for your time and help. If its just a Moon Phase error I suppose I can live with that, but an error like this does have the potential to be catastrophic for me if it happens again. Besides checking for meters and waveforms, are there any other precautions you could recommend to me to hopefully avoid this problem in the future?

8

If you need to do that, I strongly suggest exporting as WAV. Every single encoding of MP3 loses quality. But that sounds like an issue with screen refresh on your computer. Export does not increase the waveform height unless you turn up the -…+ gain sliders on the track.

Windows Update while recording from a web cam and audio at the same time could be enough to cause dropouts in the recording (and so a shortened waveform). Here is a long list of tweaks to consider that “might” prevent a recurrence: Managing Computer Resources and Drivers - Audacity Wiki .


Gale

9

I believe the default Audacity sound meters are too small. You can make them much larger by clicking on the right-hand edge and pulling sideways. The other tools will get out of the way.

As a general rule, if you’re getting meters and blue waves, then you are getting a recording. They tell you a lot about the health of the system.

Koz

10

It’s been working absolutely fine for me ever since I began with it, but, while recording an audio segment for a video project this past Saturday using a conventional microphone…

What does that mean? Do you mean you weren’t using a “conventional microphone” when it was working fine?

Pyle PDMIKC Professional Conference Microphone

Microphones with XLR connectors are low impedance balanced and they don’t properly interface directly with a computer (high impedance unbalanced).

If you are going to use any good microphone, you generally need an audio interface with XLR mic inputs, or you can use a mixer plugged into your soundcard’s line-iinput, or some mixers have USB outputs.

Another option is a “studio style” or “podcast” USB microphone.

I found one of the files horribly distorted. The first clue that something was wrong was that the waveform in the topmost track was missing.

Do you mean the top half of the waveform is missing? That’s usually a hardware/soundcard problem.

… because usually the audio still works and if I truly need the waveform exporting the file out and back in as an MP3 usually brings it up)

MP3 encoding can change the shape of the waveform, but a high-quality (high bitrate) MP3 shouldn’t change the sound at all. But, MP3 is lossy compression and it should be avoided until the last step if you want to distribute in MP3 format.

When I tried to playback the audio, it was extremely quiet, I had to Amplify it up to 40 dB to be able to hear it at a normal level,

That could be because you are plugging a low-impedance mic into a computer.

The audio on that file represents a very important segment I am loathe to lose. Can anything be done to salvage it? And are there any steps I can take to ensure this doesn’t happen again?

Computers are unrelaiable. If you have a computer dedicated to your “home studio”, it can be fairly reliable. And in a studio environment there you can usually “take 2”, if there’s a problem. Once your are familiar with your hardware & software, you’ll probably be OK 95% percent of the time…

For a critical “live” recording, it’s best to use a portable solid state recorder, or even a cassette or VHS recorder, or two systems recording in parallel.

The only things that were running on the computer was Audacity and Windows Movie Maker. (for the webcam recording) If such is the case, why was the webcam audio not similarly affected?

That’s another potential problem. You shouldn’t multitask while recording. You’ve got a multitasking operating system, but only one data bus, one CPU (perhaps multi-core), and probably only one hard drive. Even if you are only running one application, Windows is multitasking in the background.

When you record audio (or video) the digitized audio streams-in at a constant rate, andit goes into a buffer (memory… a small “holding tank”). When the operating system gets around to it, it reads the buffer in a quick burst and writes the data to the hard drive. If it doesn’t get around to reading the buffer in time, you get buffer overflow and a “gitch”. The same thing happens in reverse during playback, and the danger is buffer _under_flow.

Note that the CPU doesn’t have to be 100% maxed-out to have a problem… All it takes is for an application or driver to “hog” the CPU for a few milliseconds too long, and you get a glitch. Windows Movie Maker may be a bigger hog than Audacity. It’s also feeding pre-compressed audio/video into your computer, and it might have a bigger buffer.