Batch processing files with Audacity

In my last post Using Text to Speech online tools to create audio files for Arduino projects I had some info about online text to audio sites I have been using to create audio alert files for projects. The files produced by ttsmp3.com seemed to have a lower audio level than I expected. I found I could run all the files through a batch process in Audacity to normalize them. I spent a lot more time trying to find out how to do it so I’m making this quick post so I have the info for next time.

I was running Audacity 2.1.3 which is now an old version. The terminology and location of the feature changed in 2.3.0. Essentially the pre 2.3 version seems to call it ‘chains’ whereas it became ‘macros’ in 2.3. I’ll include info for both as I made notes for the older versions first.

The relevant info is available on the Audacitiy site.

There are two parts to the process

1. Create a chain/macro with the processes that will be run during the batch process. This only needs to be set up once.
2. Select files and run the task.

There are a lot of other changes that can be included. I’ve also added Mono to one as I found some of my files created another way were stereo and others mono. My project only had a single speaker so I converted them all to mono for consistancy.

Pre 2.3 version

In these versions the batch process is referred to as a chain.

To create a chain

• Go to File
• Select Edit chains…
• Add button
• Set a name, e.g. Normalize to -0.1dB
• Insert Normalize – Tweak settings if desired. I didn’t

• Insert ExportMP3 – This is required otherwise the files are not saved

To use the chain

• Go to File
• Select Apply chains…
• Select the chain, in my case ‘Normalize to -0.1dB’
• Select Apply to files

• Browse to the file folder and choose files

• Select Open
• Converted files will be placed in a folder called cleaned inside the folder of the selected files

Current version

In later versions it is called a macro.

To create a macro

• Go to Tools
• Select Macros…

• New button
• Set a name, e.g. Normalize
• Insert Normalize. There is also an option ‘Normalize (Macro_Normalize)’ that I have not tried

• Insert Export as MP3 – This is required otherwise the files are not saved

To use the macro

• Go to Tools
• Select Macros…
• Select the macro, in my case Normalize
• Select Files
• Browse to the file folder and choose files
• Select Open
• Converted files will be placed in a folder called macro-output inside the folder of the selected files

Before and after

Here is a before and after shot. The before is the one at the top.

As always, let me know if you find inaccuracies in my info.