As online sound broadcaster I had to personally put to the test the differences between AAC and AAC+.
First know that AAC and AAC+ is the replacement for MP3. AAC is designed for high-bitrate applications ex. 128 Kbps or better and AAC+ for lower-bitrate applications 96 Kbps or lower. Please note that I have based these numbers on the following:
1. Many encoders for AAC will provide bitrate options from 16Kbps - 320Kbps
2. Many encoders fro AAC+ will provide bitrate options from 16Kbps - 96Kbps
My concern for testing both versions of the AAC format came when we decided to broadcast in true CD quality onine at
http://www.BeHeardRadio.com. We knew that to a complish CD quality using MP3 we will need to use 192Kbps a starting point, being 256Kbps the right bitrate to give use the quality we where persuing. AAC allows us to have CD quality at a lower bitrate. The question that came to mind was which of the 2 formats (AAC and AAC+) could deliver CD quality at the lower bitrate?
While testing the different bitrates a little surprise came to light! - Please note that the codec we use to test our audio files is from MainConcept
16Kbps AAC+ Peforms better than AAC
24Kbps AAC+ Peforms better than AAC
32Kbps AAC+ Peforms better than AAC
48Kbps AAC+ Peforms better than AAC
56Kbps AAC+ Peforms better than AAC
64Kbps AAC same or better than AAC+
80Kbps AAC Peforms better than AAC+
96Kbps AAC Peforms better than AAC+
128Kbps AAC Peforms better than AAC+
You can see that AAC performs better than AAC+ if you use a bitrate higher than 64 Kbps. At 64Kbps quality is near-CD but not CD quality! it is clear that AAC+ is great for limited bitrate are great quality compare to any other format. In other words, 48Kbps AAC+ is equal to 80 Kbps MP3.
It was clear to us that the right bitrate to truly achieve CD quality is 128Kbps AAC. This bitrate compares to MP3 at 192Kbps or better.
Conclusion: if you are planning to broadcast in CD quality either use AAC at 128Kbps or MP3 at 192Kbps or better! AAC+ is great for movies and near-CD quality at 48Kbps-64Kbps using any bitrate higher than this and AAC will perfomr better and AAC+.