Compress audio files on your Mac, offline
By Himanshu Ranjan · Updated 8 November 2026
To make an audio file smaller on a Mac, select it in Finder, hold the right Option (⌥) key and choose Compress › Compress to 128 kbps for music, or Compress › Compress for voice (64 kbps mono) for speech. FileDial saves a new, smaller copy beside the original, shows the size before and after, and never uploads your audio.
How to do it with FileDial
- Select the audio files you want to shrink in Finder.
- Hold right ⌥ to open the dial.
- Choose Compress › Compress to 128 kbps, or Compress › Compress for voice (64 kbps mono) for speech.
- Check the size before and after on the result card; the original stays beside the new copy.
Your original file stays untouched. The result is saved beside it, and every result has Undo.
Which option to pick
| Tool | Use it when |
|---|---|
| Compress to 128 kbpsCompress | Music or mixed audio needs to be smaller. Saves a new 128 kbps copy beside the original. |
| Compress for voice (64 kbps mono)Compress | The file is speech only, like a lecture or voice memo. Saves a new 64 kbps mono copy. |
How bitrate and mono affect file size
For compressed audio, file size depends almost entirely on bitrate and length. Bitrate, in kilobits per second, is the amount of data spent on each second of sound, so halving the bitrate roughly halves the file. The question is how low you can go before people notice.
128 kbps is a long-standing middle ground for music and mixed content: small enough to email or store in quantity, and generally fine for casual listening. Critical listeners and anyone keeping a master copy should stay with a higher bitrate or a lossless format.
Speech is much more forgiving. A single voice has a narrower range than a full band, and it carries no stereo information worth keeping, because the listener hears the same voice in both ears. Folding stereo to mono and encoding at 64 kbps is therefore usually fine for lectures, interviews, voice memos, meeting recordings and spoken-word drafts. It is not a good choice for music, where cymbals and stereo width suffer noticeably.
Compression is lossy and one-way. Each time a lossy file is re-encoded it loses a little more, so compress from the best source you have, and keep the original if you might need it again. FileDial keeps it automatically by saving a new copy.
- Music, mixed audio or anything with stereo effects: Compress to 128 kbps.
- A single speaker or a conversation: Compress for voice (64 kbps mono).
Why not compress audio with an online tool
People usually compress audio because they need to send it somewhere: a recorded lecture for a study group, an interview for a transcriber, a draft mix for a collaborator. The irony of an online compressor is that it requires uploading the full-size file first, to a service you have no relationship with.
The FBI Denver Field Office warned on 7 March 2025 that free online document converter tools are increasingly used to spread malware. The conversions work, but returned files can carry malware leading to ransomware, and sites can scrape personal data including identity numbers, banking and crypto details, emails and passwords. The warning was aimed at document converters, but it applies just as sensibly to any site that processes your files.
FileDial compresses on your Mac. Nothing is uploaded, and every tool works with Wi-Fi off.
Other ways to do it on a Mac
The Music app can re-encode tracks if you set its import encoder and bitrate in Music › Settings › Files › Import Settings, then use File › Convert to create a new version. The copy goes into your Music library, and the files you convert are added to the library as well. QuickTime Player can export an audio-only M4A with File › Export As › Audio Only, though it does not let you pick a bitrate. GarageBand can share a project as a compressed file with a quality setting.
FileDial is the better fit when you have a batch of recordings, when you want a voice-specific mono preset instead of picking settings, when you want each smaller copy beside its original rather than in a library, and when you want to see the size before and after with Undo on every result.
Questions
Will compressing audio overwrite my original file?
No. Both compress tools save a new copy beside the original, so you keep the full-quality file. The result card shows the size before and after, and Undo removes the new copy.
Is 64 kbps mono good enough for a podcast?
For speech-only recordings, 64 kbps mono is usually clear enough, which is why FileDial offers it as Compress for voice. If your episode has music beds or stereo effects, Compress to 128 kbps is the safer choice.
Can I compress a whole folder of recordings?
Yes. Select all the files in Finder, hold right ⌥ and choose the compress tool once. FileDial runs it on every selected file, and a watched folder can run a recipe on anything you drop into it.
Does compression happen on my Mac or in the cloud?
On your Mac. FileDial never uploads files, and every tool works with Wi-Fi off. That means your recordings stay private even on a plane or an unreliable connection, and no file names, paths or contents are ever sent anywhere.
Can I try it before buying?
Yes. FileDial has a 1-day free trial with every tool, no card and no account. After that it is $20 once for a lifetime licence on 2 Macs, with a 14-day refund.