HE purpose of this study was to find the best algorithm, one that would combine high quality at low bitrates and works everywhere. It was first written in 1998 when phoneline speeds were still a major bottleneck in streaming high quality music. I was asked to create an internet radio application and I was looking at the best codec around. MP3 with various settings such as variable bitrate and joint stereo would sound acceptable in low-fi equipment at ~90kbps but that was far ahead than phoneline speed. Other codecs would sound better but player availability was an issue. So I started doing comparisons with my friends (and younger relatives who had better ears) and keep notes which lead to writing this article.
We are now beyond phone line speeds (128kbps is a barely demanding bitrate) but I always imagined all those years that it would be great if someone could write a codec that freely provided high quality audio at very low bitrates. MP3 was the most compatible but sounds good at high bitrates; AACplus was almost there by it wasn't free. WMA and Real Audio were too tied to specific software and not free. Vorbis was a bit better than MP3 but hard to play to anything else than a PC.
Then a few weeks ago I found an article about the Opus Codec. It seems that my quest is over. Opus sounds great at extremely low bitrates and its free and it seems there is a great interest around it as Mozilla has already supported it in Firefox, Foobar2000 can now compress audio in Opus and Google seems to be noticing it which means we may see it supported in Android.
I am not sure if I can assemble my original testing team but if I do we'll give Opus a test and really finish this. For the time however, I can summarize to the following: Opus is free and provides high quality, MP3 is the most compatible, AAC is not free but it is quite widespread and provides good quality and multichannel audio.