Everything seems to be claiming “HD” these days. Of course the dilution of the term renders it less and less meaningful. Currently it seems to be the name of choice for iPad applications. It’s not as if the iPad or iPhone are high resolution devices. Their dot pitch is higher than some previous Apple hardware but it’s nowhere near what some manufacturers are kicking out. The only thing that makes it sort-of-HDish is that 720p/1080i are often rendered to a device with 768 pixels vertically and so in a 4:3 aspect ratio, it is at the lowest end of “HD ready”. The trouble is that to fit a 16:9 aspect ratio picture in 1024 pixels width, you’re only going to use 576 pixels height, and we here in Europe know that as “PAL”… It’s higher D than the 480 of NTSC but it’s half what REAL HD video is. On the upside it means your DVD resolution sources are going to look mindblowingly good on such a small screen. Interestingly it also means you have 200 pixels space on 16:9 content which you could use for the controls, subtitles, Social networking status updates.. oh wait, no multitasking without a jailbreak. I digress…

Anyway, this week saw me purchase a new pair of headphones: Bower & Wilkins P5. and this leads me onto the subject of HD Audio. Believe it or not, audio is far more guilty of HD travesty than video.

Many were sold DVD on “Better quality audio” but really it was the multichannel equivalent of MP3. 6 channels encoded into 384 or 448kbits per second: about 128kbits stereo or the bitrate of a fairly naff MP3. Fortunately there’s some economy of scale so it sounds rather better than a 128K MP3 but we’re still not talking HD. Even at the maximum bitrate allowed by AC3 – 640kbits/s, some soundfields just didn’t map well to Dolby Digital.

Fortunately there was a saviour in the shape of Digital Theatre Surround (DTS). They allowed up to 1.5Mbit for core DTS and that gave more channel separation and dynamic range. CD is encoded losslessly at 7kbit/channel. In fact, DTS soundtracks for films in cinemas were supplied on CD originally. Music DVDs quickly began to offer DTS soundtracks. DTS can also live happily on a CD Audio track (PCM Stereo 16bit, 44.1kHz samplerate) but obviously in order to hear it, your CD player needs to be connected digitally to a DTS capable receiver otherwise you hear pink noise and you could damage your speakers. By doing this, you can store 5.1ch audio in pretty good quality on a CD. A few artists started to exploit this too.

Some thought DVD had promise as a better-than-cd-quality audio source and DVD-Audio was born. Unfortunately it didn’t catch on. Many people were perfectly happy with CD sound. A few weren’t and these purists still preferred vinyl. DVD Audio offered Multiple channels at 96kHz and a maximum of 192kHz samplerate in stereo at 24bit resolution. There was compression used, but it was lossless – Meridian Lossless Packing (MLP). It has about the same amount of compression as FLAC. Usually a DTS or PCM option was provided on the disc as well so that it would work in ordinary DVD players too. The problem is that they restricted the format to the analogue domain. You had this superb source but all the decoding was done inside the DVDA box and output via the analogue connections. So the consumer only knew as much as their DVDA player or the music publisher chose to tell them (usually very little) and so you could buy a DVDA disc with 20bit 48kHz audio for the same price as a 24bit 192kHz disc. As the consumer you couldn’t see any details about the source’s quality when you bought it (necessarily) and certainly the players I owned never gave the secret away but some discs definitely sounded better than others. Would you feel ripped off if you bought something with little discernible difference from the CD for twice the price? I think you would. Result: DVD Audio fails as a format.

Sony step in with Super Audio CD. If studios use Sony digital mastering then they almost get this free. Rather than recording 24 bits of data at each sample, they record a single bit but they sample very much faster: 2.8MHz. The result is a stream with more data than 96kHz/24bit but with a simpler, more linear process with less latency that some claim sounds more like analogue than even 192kHz/24bit audio. The catch here is that unless your DAC does native DSD processing then it gets converted to PCM and then analogue. This muddies the water somewhat. You haven’t heard SACD for real until you’ve heard SACD without a PCM stage. I wonder how many people have actually heard SACD without a PCM intermediary stage? There’s very little SACD material around. It’s very niche.

Welcome to the 21st century. Blu-ray Disc won the format war and this may end up being a good thing. Why? Blu-ray has 25 or 50gb per disc of storage, baked in support for 6CH LPCM, DTS HDMA, DD TrueHD and an audio disc profile.. One interesting little nugget is that DD TrueHD is the very same MLP that was in the DVDAudio spec, meaning that Blu-ray Disc is built with the capacity for any existing player to produce high definition audio and output it digitally via HDMI at very high bitrates.

What this means is that it’s entirely possible for all Blu-ray Disc players to be audiophile music players. This is important because soon there’ll be one in most homes and so discs will just work. That’s one heck of a captive market. There’s no excuse with Blu-ray Disc not to provide uncompressed audio with your concert.

A friend of mine asked me why there are no BD audio only discs – well, there are. I have a couple of them, but they find it hard to think of ways to use all that space.

Nine Inch Nails Ghosts comes on four audio CDs or one BD at 96/24 stereo LPCM. That’s a beautiful use of 17Gb of storage. Two audio CDs at 192/24 stereo LPCM would fit in the same space (Super release of War Of The Worlds, anyone?)

One caveat. These numbers are all assuming that the source the track is encoded from is better than that offered. If you bump up the bitrate to make it look better. It probably isn’t going to sound any better since good players will effectively do that anyway. There’s no point in storing something you can recreate with a simple algorithm. It just takes up more disk space.