Dfiler, it's interesting that you seem to measure sound quality across various mediums using vastly different compression algorithms by a single arbitrary number, the "bitrate":
there is probably a near unanimous opinion, at least among people who are familiar with bit-rates, that 128kbps and lower is not "HD" audio.
As if the quality and efficiency of the particular perceptual codec used is immaterial. Me, I'm different, I don't worry about which is the "correct" bitrate number to be above, but rather the end result's distortion, frequency response, channel separation, signal to noise ratio, dynamic range, and the possible audibility of any artifacts. The bitrate used is entirely immaterial to me since I'm aware that psychoacoustic testing of different perceptual coders have shown that some advanced designs using spectral band replication (or SBR, which HD radio does
by the way) can sound superior
to for instance MP3 or AAC using only half
By combining SBR technology with existing (modified) codecs, independent tests in subjective, scientifically controlled listening conditions conducted by the EBU found them to be "virtually transparent at 64 kbit/s".
[I assume everyone here understands "transparent" means audibly indistinguishable to humans compared to the original, uncompressed source material.]Source.
[Read the end of the third paragraph on page 1, the summary.]
HD radio uses a proprietary compression scheme developed by Coding Technologies called HDC with SBR and PS, parametric stereo, (based upon MPEG-4 HE-AAC v2). Because it is proprietary I don't know of any third party scientifically controlled listen studies, however HE-AAC v1
(aka aacPlus on this chart), without
the advantages of PS that v2 and HD radio have, has
been independently evaluated by the EBU and others and fairs very well compared to all other codecs tested using MUSHRA scales, even at the embarissingly low bitrate of only 48 kbps,
fooling some listeners in some trials that they were hearing the original source:
Keep in mind the data in this chart is not for HD radio but rather an inferior
system, HE-AAC v1, which doesn't have the advantages of PS which HD radio (which is based upon MPEG-4 HE-AAC v2) does