What makes Audacity slow?

Hi, when I import some audio tracks (audio language track of a film) into audacity, it’s very slow compared to other files.

For example, if I import into Audacity (2.1.0) a mp3 song that is 10MB and 5 min length, it’s very fast and responsive. Nevertheless, if I import something like an audio track from a film (AC3 700MB and 2h length), it’s so slow compared to the mp3’s. So, what makes Audacity to be really slow?

  1. Is it the length of the audio track?

  2. Is it a large file, like 20MB or larger?

  3. Is it the MB/s of the file (high bit rates)?

  4. When it should be slower: if I add a 10 min length 300MB audio file, or if I add a 30 min length 40MB audio file?

    I’m talking about these aspects:

A) When you zoom in and move from one position to another in the track… (for example, this is so slow when working with audio tracks of films, and I don’t know if it’s because of the length or the size or a high bit rate)

B) When applying effects to a selected audio track. This is CPU intense (I guess), but I don’t know if it’s only the length of the track what affects adding an effect or the MB/s too, or the MB of the selected track.


PD: I’d like to know what piece of hardware slows Audacity too. I pretty sure that if I used an SSD, some of the stuff I’m talking about would be lightning fast.

Audacity does not work directly on the “audio file”. When you import an audio file, Audacity extracts the audio data from the audio file and makes a copy of it. Audacity then works with the copied data. The original format of the audio file is therefore irrelevant in this respect. However, the sample rate and length of the imported track will make a difference to how long it takes to perform an operation (process) the track because long and/or high sample rate tracks have more data to process than short and/or low sample rate tracks.

The size in MB of the imported file is not the important issue with regards to processing speed. The important factor is the size in MB of the audio data after it has been decoded and copied into the project.

The amount of data in an audio track (in an Audacity project) depends (only) on the number of samples, the number of audio channels (mono / stereo) and the number of bits per sample (the sample format). The size of that data can be calculated (in bytes) as:
Number of channels x sample rate (samples per second) x length (in seconds) x bits per sample / 8.

Thank you Steve.

I have an i7-4700MQ, that is a quad-core 2.4GHz processor, with hyperthreading, and can reach 3.4GHz. So, I can’t improve much the CPU part here.

I’m more interested in the HDD intense tasks. That’s what really slows down the experience. Importing is pure HDD performance. But once you’ve imported the audio file, Audacity still goes really slow when working with language tracks from films. It’s slow when zooming in, moving within the track (from one position to another), and that kind of stuff.

So, in these cases:

  1. Is it that I’m working with 2h audio files?
  2. May be is it the MB/s of the audio file?

What is the limit for Audacity to work well if you have an HDD?
Considering that most HDD are very similar in performance, this should be an objective question.


When 2.1.1 is released (we hope in a week or so) it should be faster moving around and editing in the audio visible at any one time in the project window.

Zooming and fitting in longer tracks is slow for a variety of reasons. This is yet to be fixed.


Wow, great news, Gale!