WWW FAQs: What bitrate should I use for my audio files?

2006-08-08: The right bitrate depends on your audio. So I'll look at several different needs and make appropriate recommendations for each.

In the article how do I embed sound and music in a web page? I recommend the use of the MP3 format. That's because MP3 is the most widely supported of the well-compressed audio formats. But MP3 files can have several different bitrates, and there's also the question of mono versus stereo. What's best for your needs?

Spoken Word

For spoken word performances, including talk radio, speeches, poetry and sermons, a high bitrate is a waste of bandwidth that will frustrate users with slow connections and rack up high charges with your web hosting company. And stereo is useless here - one person is speaking and we don't need to hear them move around the room! You can go as low as 24kbps (kilobits per second), mono, and still keep excellent speech quality. At 24kbps, a full minute of speech takes up only 180K (180,000 bytes) on disk. And even a good dialup telephone connection can easily keep up with that.
MP3 was designed for audio in general, and doesn't do an optimal job of "squeezing down" speech. The Speex Codec sounds good at much lower bitrates. But most webmasters will want to use MP3, because most website visitors already have the necessary player software.

Acoustic Solo Performance

A solo performer on an acoustic guitar can sound quite good at as little as 32kbps. You may find that your performances require 48kbps for every nuance to be heard clearly. Once again, we don't need stereo. At 32kbps, one minute takes up roughly 240K on disk.

Group Performance - Low Quality

Uploading demos of a full band? You'll be able to hear a song reasonably clearly at 64kbps mono... but you'll definitely know it's not a high-quality recording. 64kbps mono sounds rather "AM-radio-ish," and should be used only as a low-speed alternative download for users still stuck with telephone modems. Some artists have tried giving away 64kbps files and charging for better-quality versions. The problem is that listeners get the message that your band just doesn't sound that great.

If you do go with 64kbps, don't bother with stereo. The space requirements will go way up, and "AM stereo" isn't a huge improvement over AM mono!

One minute of 64kbps mono will take up about 480K on disk. At this bitrate, dialup modem users will have to wait for the entire song to download. Broadband users will have no problem streaming it live.

Group Performance - High Quality

If you want to impress people with a well-produced, professional song, go for 128kbps, preferably in stereo. For near-CD quality, 256kbps stereo is also an option.

128kbps stereo recordings take up 960K of disk space per minute (nearly a megabyte).

At such high bitrates, dialup modem users will probably give up. Broadband users will still be able to play the song as it streams down from your server. However, if you have many listeners at any given time, your total bandwidth requirements will be quite high. And that can mean high hosting bills. Even if your users don't listen simultaneously, you may still have overall data transfer limits imposed by your web hosting company. See the article how much bandwidth/data transfer does my site use? to understand the issue better.

Don't Exceed The Source Material

There's no reason to use 128kbps stereo if the original performance is a talk show or even an acoustic recording by a single musician. In the latter case, 64kbps mono is approaching overkill. And every time you increase the bandwidth requirements, you risk higher hosting bills and create frustration for users with slow connections. So, don't do it unless it's worth it!

Watch Out For Chipmunks

If you export an MP3 file at a low bitrate such as 64kbps from the generally excellent Audacity program, you may find that your recording sounds like a roomful of chipmunks in the XSPF Web Music Player or any other Flash-based player. This is because of a compatibility problem: Flash is picky and only supports a handful of sampling rates. This doesn't mean you can't use a low bitrate, but you'll have to do a little more work. See the article why does my MP3 file sound bad in Flash player? for a complete solution.

Go Forth And Broadcast

You're all set to save your MP3s at the correct bitrate. For more information, see the article how do I embed sound and music in a web page? and the article how do I start my own Internet radio station?

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