My article for Radio Guide in Jan 2007. explains why you need audio processor specifically designed for digital audio broadcasting, and what are the different requirements between analog and digital transmissions in regards to audio processing.
Abstract: With IBOC (aka HD Radio) gaining momentum, many stations are deciding to include a second channel (HD2) and even third (HD3) as an alternative and/or additional programming to their main channel. Many broadcasters are also looking at streaming to the web as royalty fees are now clearly regulated and more people are using on-line multimedia services than ever before.
When it comes to processing for these new services – especially if they have different programming than the main channel – it is tempting to use your old FM processor that has been sitting as a backup. But that would be a mistake. In this article we will try to explain why and what are the requirements and the differences in processing for analog FM and digital channels.
Key words: digital broadcasting, HD Radio, IBOC, digital audio processing, dynamics processing, clipping, look-ahead limiting, pre-emphasis, codecs, perceptual coding