I just read a response by Mark Waldrup, Ph.D., to an article on HD Audio that appeared in SmartHouse News. Mark is the chief engineer at AIX Records. He's also the founder and director of the High Definition Surround Music Association (HDSMA), a non-profit dedicated to supplying accurate information and demos of HD Audio.
In his comments, Mark answers "What is HD Audio?"
Here's the definition the HDSMA prefers - "HD Audio is music or sound that is captured from the acoustic source at or near the fidelity of human hearing."
Mark explains that this means recorded/reproduced sound that has a frequency response of at least 20 kHz and a dynamic range of around 124 dB or more.
He goes on the say that the only consumer formats capable of supporting HD Audio fidelity are SACD and DVD-Audio. However, most of the SACD and DVD-Audio discs released are not true HD Audio because they are performances that were recorded before HD recording equipment was available. The analog tape equipment is only capable of a frequency response of 18 kHz and a signal to noise ratio of 72 dB, which is equivalent to a sample rate less than 44.1 kHz and a bit depth of 12 bits. Mark explains that even though you re-record it at 24 bit/96 kHz, it won't sound any better than the original analog master tape.
Mark also mentions that the HD in HD Radio doesn't stand for high definition, but is instead something like "hybrid digital." I agree that this is only adding to consumer confusion, especially when you consider that the resolution of HD Radio is only 64 kbps, which is half the bitrate of the worst quality MP3 or iTunes downloads available today.
Personally, I think the marketers have really screwed things up. It probably started when the marketing folks at Microsoft referred to the quality of their WMA encoder as "CD quality" when the bitrate was set to 128 kbps. The marketers probably know that if this kind of thing is repeated enough people will just accept it as fact (hmmm, that sounds familiar). Other companies simply play along. Now MusicGiants refers to their losslessly compressed tracks, which are really CD quality, as HD audio to distinguish it from the lossy encoded tracks available from the big music services like iTunes. Their 24 bit/96 kHz tracks are now referred to as "Super HD Audio". According to Mark, MusicGiant's "Super HD Audio" isn't even HD Audio because it was re-purposed from the original analog master tapes instead of recorded with actual HD equipment.
I have listened to 24 bit/96 kHz recordings (both 2 channel and 5.1 surround) from MusicGiants and they do sound better than the same recordings that I already owned on CD. However, I haven't had a chance to listen to the HD Audio offered by AIX Records. I first read about Mark (Dr. AIX) last Winter and am still waiting for them to launch their itrax.com website, which will offer HD Audio downloads. I thought their website was going to go live in June. I wonder what is holding them up... Anyhow, I am looking forward to hearing what Mark calls True HD audio. Hopefully they will have a diverse catalog with a lot of great artists to choose from.