To increase encoding quality, the broadcaster can both lightly process the audio on the digital side and then can set a volume offset flag to increase the level of audio at the HD radio receiver to still sound "loud" and to have the perceived volume level differences between the analog and the digital are minimized. This eliminates having the listener turning up the volume when the HD signal kicks in. Sadly many stations don't do this and either compress their digital audio the same way as their analog audio to compensate for the differences or they lightly compress and don't know how to apply the volume offset and the digital feed sounds too quiet in comparison, not satisfactory or convenient for listeners in a vehicle environment. Remember there is no FM stereo "hiss" with HD radio. There are supposed to be engineers at these stations, sometimes I'm floored as to how inferior audio and time delay settings can go on for months/years before being fixed or never fixed, at many of the "big" Chicago stations I listen to. And then the HD radio standard gets the blame when the broadcaster themselves can control so much. Remember on the HDTV side, a few years ago, when all the macro-blocking used to be seen when transitioning between scenes or fast action, nowadays that is significantly reduced and it's still the same ATSC 19.2 Mbps MPEG-2 signal the broadcaster uses, and everyone was blaming the bitrate and MPEG-2 and really it was the pre-processing quality and compute power were the main issues.