Discontinuities / Shifts in Audio

I’ve encountered a problem with almost all of my audio files having what I’ll refer to as a “discontinuity” of the sound wave / pattern. During playback I’ll hear a static like pop or click. At least half the time I can zoom in the timescale and readily find a place where the sound wave has a break point where it shifts up OR down vertically, continues the original pattern very briefly, then shoots vertically down OR up - returning to the “original” path of the wave form. I’ve also equated this to having your shoulder pop out of socket. I’ve attached a few screenshots to illustrate.

When I zoom in, if I select a segment which include the entire discontinuity and bit of the wave immediately preceding and following I can use the Effect; Repair option and smooth it out (or pop it back into it’s proper position). This always fixes the problem when the defect is obvious, and the click / pop is gone. But sometimes only one “leg” pops up or down and there seem to be other less visually obvious manifestations.

I find these in my raw voice (narration) recordings. I’m recording directly in Audacity with a condenser mic (CM25) using a Focusrite 2i2 on a high end laptop. My recording booth is reasonably quiet, I consistently have a room tone below -45 dB. These glitches seem to occur randomly but usually mixed in with speech. Post recording, more of these seem to creep in as I perform various edits such as truncating silence, noise removal or EQ.

This seems to me to be a software issue. I’m speculating that it might have something to do with the way Audacity stores and manipulates chunks of sound in small files. If it were my recording equipment / chain, I would think such glitches would not increase in number during post recording engineering.

Has anyone else seen, and resolved, this issue?

You may have two problems, lucky you.

A straight discontinuity, tiny straight, flat line with no up or down motion usually means the data from your performance was interrupted either through defect or the machine can’t keep up the Scarlett bitstream.

A straight vertical offset, either up or down, can (usually) mean a hardware problem such as a defect where the battery voltage that runs your Scarlett is getting into the sound channel.

A combination of the two is very rare, but could mean a gross periodic failure such as a loose USB connection.

It’s so rare, that I’m not sure I can think of a test. Can you try the Scarlett on another computer? Can you try a different USB connection?

You should know that it’s completely forbidden to run USB audio through a hub or other distribution hardware. Computer home runs only.


As Koz noted, that is not a usual “can’t keep up” glitch, so the first thing that I would check is that the drivers are the latest available for your operating system. http://us.focusrite.com/usb-audio-interfaces/scarlett-2i2/downloads

Post recording, more of these seem to creep in as I perform various edits such as truncating silence, noise removal or EQ.

Truncating silence sounds like it could be “risky”, depending on how you are doing it. Or if you select part of a file and apply an effect to the selection, you might get a discontinuity.

To minimize the “normal” can’t keep-up glitches, try Edit → Preferences → Recording, and increase your recording latency.

Make sure you are not running any other applications in the background, and you may have to turn-off Wi-Fi and your anti-virus.


Some background - A faster computer usually helps this sort of thing, but it’s not that your computer is not “fast enough”. It’s that you have a multitasking operating system so the audio can’t be read “smoothly and constantly” onto the data bus and to the hard drive. (Even if you are running only one application, Windows is doing stuff in the background.)

The digital audio comes goes into a buffer (a “holding tank”) at a nice-smooth constant rate. Whenever the operating system gets around to it, it reads the buffer in a quick burst. If some other application or driver is “hogging” the CPU & data bus for a few milliseconds too long, the buffer overflows and you get a “glitch”.

A bigger buffer results in more latency (delay). As long as you are not monitoring yourself through the computer, a few extra milliseconds of delay is not an issue and a big buffer is a good thing. Your Focusrite has direct zero-latency monitoring, so you shouldn’t need to monitor yourself through the computer while recording.

When you play-back audio (or video) the buffering works the other way around. The application writes data into the buffer in quick bursts, and the audio (or video) flows-out at a smooth-constant rate. In this case, if the operating system doesn’t get-around to re-filling the buffer in time, you get buffer underflow, and again a “glitch”. And again, a big buffer is a good thing.

I think you will find the same recorded glitches if you use other software, until you address the issues with your equipment or your computer.

Glitches will increase if you edit a track containing DC offset. Your first step should be to select the whole track then use Effect > Normalize… to remove the DC offset.

Thanks for all the great feedback. I did try using another software for recording (a trial version of Adobe Audition). While the number of occurrences seemed to go DOWN, there were still a few. I’ll try the suggestions outlined here soon. Thanks again.