Recorded podcast - stuttering

Audacity Help Forum GNU/Linux
1

Hi all,

I’ve recorded and produced 13 podcasts episodes in Audacity on my current system, and until now I’ve had no problems whatsoever. But yesterday I was about to start editing my 14th, and I found that the recording (made the day before) has lost some quality. It’s gone all stuttering and poppy (not sure if those are the right terms), and also the timeline is distorted (about 20 seconds too short on a 50 minute recording). The funny thing is that the quality is fine in parts of the recording, especially towards the end. Here’s a short sample from one of the noisier parts:

FLAC | WAV

I searched around for other similar problems on the forum, but I wasn’t able to figure out whether this is the same problem as anyone else is having. I’m posting here looking for any precautions I can take to avoid these problems in the future, or steps I can take to isolate the problem.

My setup

  • I’m running Ubuntu 12.04, with PulseAudio (standard install of Ubuntu, haven’t changed anything here).
  • I have a Samson Q2U USB microphone, and I’m using Audacity 2.0.0 installed from the Ubuntu Software Center (standard apt repository I suppose).
  • The computer is a pretty standard 3 year old desktop Acer with an i5 processor and 4 gigs of ram, no dedicated soundcard, mixer or anything like that.
  • I record my own voice locally in Audacity while interviewing a guest over Skype (2.2.0.35-0maverick1) with video (video is not recorded). For redundancy, I also record the conversation using Skype Call Recorder (0.8+git.1-0ubuntu1~precise). Besides that the only thing I typically have running at the same time is Chrome with a few tabs.
  • After recording, I save the project to an NTFS hard-drive (I occasionally want to access my storage from the Windows dual-boot). I’ve done this several times before and haven’t had any problems, as the Audacity’s temp (recording) folder is on the Ubuntu partition.

Here’s my partition table. The bottom one is where I saved the project (NTFS). The top one is where Audacity’s temp folder is.

➜  ~/>df -Th
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/sda5      ext4       49G   22G   25G  48% /
udev           devtmpfs  1.9G  4.0K  1.9G   1% /dev
tmpfs          tmpfs     764M  1.1M  763M   1% /run
none           tmpfs     5.0M     0  5.0M   0% /run/lock
none           tmpfs     1.9G  6.8M  1.9G   1% /run/shm
/dev/sda6      fuseblk   410G  297G  114G  73% /media/storage

My theories

…on what could suddenly have caused these problems:

  • I regularly do automatic updates from Ubuntu. Some of these could have changed something about the audio behavior on the system
  • I was busying around more with the machine than usual, using Chrome to look at some Google Docs. Usually I have Audacity and Skype in the front while recording, with Chrome running in the background.

So far, my attempts to reproduce the issue have been unsuccessful.

I’ve had a look at some resources regarding these problems, and these are the ideas on precautions I can take:

  • Avoid running Chrome at the same time
  • Increase Audacity’s process priority (I noticed in Ubuntu’s System Monitor that PulseAudio is already running with priority Very High - all others are running with Normal)
  • Save the project directly to the “local” ext4 hard-drive, not to the NTFS partition

Is this sensible? Do you think there are any other variables I should tweak? I saw there are some recommendations about HW, but I’m not in a position to make any investments there.

Many thanks in advance for any help or advice here.

2

To take this upside down, Audacity live recording or production is the test you do to see if your computer is running fast enough. If Audacity skips or stutters, it’s not.

You have the other classic symptom, too. “I’ve been doing this successfully for six months and now suddenly…”

Your computer has been slowing down as you do production and fill up the drives. They all do. You may have made it to the point the system can’t manage the data any more – remembering it’s all in real time. The system can’t put your voice on hold while it manages itself like recalculating a large spreadsheet or blurring a Photoshop picture.

So that’s my opinion. It happens to the video people, too. “How come I’m suddenly missing frames…”

http://manual.audacityteam.org/o/man/faq_recording_troubleshooting.html#skips

Koz

3

Thanks, Koz. I’ll definitely take some of those steps from the manual as precautions for the next time I record an episode.

I was trying again to recreate the problem yesterday. I fired up several programs running in the background, and ran a Skype session w/ video with another computer, trying to recreate the conditions which caused the problems. Even though the load on the machine was larger than usual, I wasn’t able to recreate the stuttering/skips. It could be some coincidence on the OS level, I suppose. I just have to hope it doesn’t happen again in the future, or get myself a dedicated digital recorder and plug that into the mix.

4

Intermittent problems are just the best aren’t they? This is me being glad I’m not you.

Windows machines can also suffer from Virus Protection that’s trying too hard. “Wait, you can’t transfer data that fast, I need to inspect it all!!!”

Do you have any USB drives in the mix? You can’t reliably do live production on USB drives…

Koz