For audio to be understood by a computer it must be 'encoded' into an audio file. This process involves taking an analog audio signal and converting it into a string of code that can be understood (digital).
This process converts continuous signals into discrete values. 'Snapshots' of the audio signal are taken at set frequency, these are called samples and the frequency is called the 'sample rate'. The standard sample rate for high quality audio is either 48000 or 44100 samples per second. the 'accuracy' of these samples is determined by the bit depth (usually 16, 24 or 32) the higher the number, the higher the quality of the audio. this then has a knock-on effect of increasing the file size.
PCM (Pulse-Code Modulation) is the name given to the uncompressed process, as a file format you will see PCM files under the wrapper of .WAV or .AIFF/aif (optimised for Apple computers)
PCM is the truest representation of audio you can find in the digital realm. However, as it is uncompressed the file sizes are often very large. For streaming purposes, Uncompressed audio would be unfeasible because of the bandwidth required to send and receive it.
For this reason, compressed audio files are preferable for streaming. Compression (not to be confused with the audio process of compression) reduces a the size of an audio file and can be either a lossy or lossless process. lossy processes mean some data is lost in the process and lossless compression can reduce file sizes without compromising the data sizes. For streaming however, lossy formats are most often used because they are the smallest files and generally sound good enough to use.
The most common forms of lossy compression are .MP3 and .AAC. The main goal of MP3 is three-fold: 1) to drop all the sound data that exists beyond the hearing range of normal people, and 2) to reduce the quality of sounds that aren’t easy to hear, then 3) to compress all other audio data as efficiently as possible.*
The compression algorithm used by AAC is much more advanced and technical than MP3, so when you compare the same recording in MP3 and AAC formats at the same bitrates, the AAC one will generally have better sound quality.* You will often see that high quality streams use aac audio and low quality audio streams use mp3... although there are ranges of bit depths available in both aac and mp3 formats which have an effect on audio quality.
Platform exclusively uses mp3 audio, ensure your audio files are in this format when uploading content.
*Source quoted: https://www.makeuseof.com/tag/audio-file-format-right-needs/