Spectragraphs: An HD Music Tool
I happened across a discussion at Computer Audiophile that has uncorked the HD Music Download world's dirty little secret. I posted the following comment…
It seems that a curtain has been pulled back and end users are beginning to understand the processes that go on during the production of a recording. I have been a long and vocal advocate on the topic of what constitutes "HD" for many years. In fact, I gave a seminar at the RMAF showing spectragraphs of tracks taken from ALL of the major download sites and DVD-R "HD" distribution discs. The qualityof the recordings varied greatly. There were tracks that extended all the way up to 48 kHz and had no clipping or apparent dynamic processing and clipping. But far too often the tracks showed limited frequency response (no frequencies beyond 22-25 kHz) and very obvious applications of heavy dynamics processing. What is being hoisted on HD fans and being reviewed in glowing terms by many writers are actually tracks that have been upsampled into "HD buckets", tracks that were recorded before HD equipment existed and tracks that ripped from discs and put out as "HD" files without verifying that they actually qualify as HD. This is done because there is better cash flow in having lots of so-called HD tracks available.
To more fully understand this, we have to define what is an HD track. I know many audiophiles do not agree with my definition but I state it this way…
A high definition audio recording is one that equals or exceeds the frequency response and dynamic range of human hearing.
Of course, there are lots of opinions on whether our ears can respond to sounds above 20 kHz and also how sensitive we are to dynamics, but that's an argument for another time. Some of the spectragraphs in this thread clearly illustrate that instruments are capable of producing audio energy above 25 kHz (however, please remember that 50 kHz is only one additional octave).
My position is that producers and audio engineers would benefit by using state-of-the-art digital equipment that can capture all of the frequencies produced by a violin or Harmon-muted trumpet (up to 50 kHz and beyond). If there is sound up there and dynamic range of 110 dB plus being produced, we should record it, plain and simple (it does require lots of expensive equipment and years of experience to get it right).
Of course, there are others that prefer to use vintage analog equipment because they prefer the "sound" of analog gear (like Cookie and T. Bone Burnett). The choices are up to the production team and the target customer. The recordings vary based on the quality and circumstances of the original session.
It's really pretty simple when you get down to the world of acoustics and equipment. In order to produce and distribute "real" high definition recordings (in any format…CD-ROM files, DVD-R files, downloadable soundfiles, Blu-ray, SACD and DVD-Audio discs), you have to start by recording a NEW production using tools that are capable of recording in real HD.
That's why the Köln Concert shows limited freqency response…or why Gaucho is limited in both it frequency response and dynamic range. The original productions of both (and lots of other older tracks) were done on analog tape. Additionally, post processing (mastering) a project for a commercial marketplace demands music that is dynamically compressed and heavily processed.
I'm not against analog tape. I've worked with analog tape for over 40 years in both multichannel and stereo. I am the proud owner of a Nagra IV-S 2-channel location recorder that boasts some of the best specifications of any analog machine (using non-standard Nagrmaster EQ). I used it for over 15 years to capture recordings of Voodoo music in Haiti, sound effects in the jungles of Costa Rica and classical music in the big room at Lucas' Skywalker ranch. But at the end of the day, analog tape has some problems. These include a high frequency bias current that hovers at around 50 kHz, limited frequency response (up to around 20-25 kHz being generous), 65-73 dB of signal to noise ratio (without noise reduction - this translates to around 12 bits or equivalent digital PCM)), speed imperfections, print-through, THD and crosstalk. I moved to HD PCM digital because it can potentially produce recording that do not suffer from those problems (although it also has issues of its own that have to be dealt with such as…aliasing, jitter, quantization errors).
If you choose to make a recording on analog tape, you have to accept the limitations of that format. Obviously, many producers have made that choice. Although, I would argue that claiming an analog source recording is HD is a dubious claim. If you like the sound (or the sound of vinyl) accept the imperfections and revel in the euphoniousness of the music. This was the standard the dominated the world of recorded music until real HD came along.
One of the posts above identified the "noise" associated with DSD's (the recording methodology of SACD discs) need to move audio bandwidth noise above the music band...effectively making SACD more standard definition than HD. Most mastering engineers "roll-off" the HF noise bringing the frequency response back into the 25 kHz range, which is decidedly standard definition and is the reason that my little company has never issued an SACD. Again, if it is a sound you appreciate or if there is a particular piece of music that is only available on SACD, I'd say go for it. In fact, iTrax offers many recordings from Harmonia Mundi that were originally tracked using DSD.
There was a small start up that offered "HD Music Downloads" called MusicGiants a few years ago. I knew the people in charge and applauded their efforts to improve the quality of downloaded files. However, I had many heated debates about there marketing as "HD" tracks that were clearly made using 24-track analog machines and mastered for vinyl or CD. To put a standard definition track into a "digital container" that has HD specifications doesn't magically transform it into an HD track. The high frequencies and dynamic range stays the same. If the original analog track topped out at 20 kHz then the 96 kHz version on DVD-A wouldn't have anything above 20 kHz as well. This is what this list has stumbled on.
Not all digital music retailers are created equal. Using Audacity, Audition or Sound Booth or other higher end professional tools (Audio Precision) are useful in determining the fundamental specifications of a given recording. They are not the only measures of a great sound track but they do contribute to our knowledge of a particular recording.