Radio stations have high standards for audio quality and standards about file formatting. In order to appeal to radio stations and reach broadcast audiences, you'll want to adhere to these standards. This guide will give you the basics about making broadcast-quality audio file formats for PRX.
When you start producing for broadcast, you should try to use WAV files throughout your production process, as these files are uncompressed and render the highest quality audio. Using WAV during the is the easiest to work with during the editing process. (To read more about compressed vs. uncompressed audio files, click here).
When you are ready to send your audio to radio stations you will need to convert the file to an MP2.
What is an MP2?
MP2 is mostly unknown to those outside of radio and certain video production industries. For many audio producers, radio broadcast is their first experience with the format.
Files encoded to MP2 are designed to reduce file sizes while maintaining a reasonable level of fidelity. Whereas an MP3 file is generally about one tenth the size of the WAV file it was created from, an MP2 made from that same file will usually be closer to half the size.
Mono vs. Stereo files
Most audio productions will benefit from having two separate channels of sound. Nearly all broadcast-ready MP2s are stereo files. One supported feature of the MP2 format is a format called intensity encoded joint stereo. This format allows for two distinct channels of sound like standard stereo, but saves disk space by looking for similarities between the two channels during the encoding process.
How do I make an MP2?
When you are finished editing your WAV file, you can convert it to an MP2 in two ways. The most recent versions of most popular DAWs have the ability to create MP2s of your file when you save or export it.
For use on PRX, we recommend converting through the free PRX/Hindenburg converter. Please not that you can only convert from WAV to MP2. You can read more here.
The PRX Exchange does not have a built-in loudness meter. However, we recommend following this broadcast standard:
-24 LUFS, ± 2 LU, audio peaks ≤ -3 dBFS for sample peaks or ≤ -2 dBTP for True Peaks
So...when I upload to PRX, how should my file be formatted?
Radio broadcast systems are designed for audio files with certain specifications, so you'll want to record and format your audio file with these in mind:
- MP2 file
- Sample rate: 44.1 kHz
- Bit rate: 128 kbps per channel.
- If you decide to create a mono MP2, it will be 128 kbps in total. But if you create a stereo (or joint stereo) MP2, the resulting file will be 256 kbps (128 kbps for each channel) in total.
- Stereo file (recommended)
- Loudness at -24 LUFS, ± 2 LU (recommended)