The encoding is what really determines everything when it comes to digital radio. Be it DAB or some other digital output, stations have to compromise with bitrates, it just is the bitter truth.
It is always a good idea to first filter the audio before encoding the signal as this helps maintain the costs. For instance if your channel broadcast happens in mono then you better compress your stereo source down to help the feed. In other words, if an encoder cannot work above 13 KHz, why should you send signals that have a frequency higher than that?
This is especially true in countries where the bitrate is horrible. Take UK DAB for instance. They still rely on MPEG-1 Layer II, which is no longer used in many parts of the world. Owing to commercial pressures and availability, several stations have had to continue with this abysmal format and reduced bitrate. Imagine transforming an FM radio station such that it uses just 32 kbps of data on DAB!
Take Jazz for instance. Reducing bitrate can drastically affect the overall composition. However, this is a compromise necessary when majority of the country has DAB encoders aren’t capable of handling DAB+ signals. Nevertheless, it is mostly a matter of testing audio on various products and receiving devices in several settings. The key is to find a compromise that manages to keep everyone just satisfied.
One key aspect you must learn is how to manage audio differently for DAB+. When your channel broadcasts via satellite television, online and DAB, you need to target DAB+ differently. Using dedicated audio processors, separate mix of routers is important. The audience using DAB+ is significantly different too. They consist mostly of those on mobile, in car or using personal sets in workplaces or kitchens.
You can receive the best success if you work beyond the processor. Ensure that the source audio is always linear PCM and that the audio is not driven too loud. Opting for the right AAC bitrate too matters.
However, be wary of over-compressing your output. With FM, you can easily increase loudness and overcome the FM hiss by masking it even at greater distances. However, this does not hold true for DAB. Here, it is governed by bit error rate and never the loudness. Hence, removing the errors is one of the rigors of compression for digital radio.