When the brain trust at HRAC asked me to post about how we define hi res audio, I rubbed my hands with glee. What an easy topic, I thought to myself. Obviously, hi res audio is a music file that is coded at 192kHz and 24 bits. Hmm, wait a second. I guess 96kHz and 24 bits sounds pretty good too. And what about a file that was recorded with big sampling and bit-rate numbers, then released to the public with small numbers; is that hi res? Actually, a good recording engineer can produce great fidelity with 16 noise-shaped bits. Wait a second. In reality, the numbers don’t really mean much. A crappy recording released at 192/24 will still sound crappy. And let’s not forget that analog tape has that sound. Hmmm, this isn’t so easy after all.
So, what is hi res audio? First, a quick review of the numbers: All things being equal (things like the gear used to make the recording), it’s true a 44.1kHz/16-bit PCM recording can provide outstanding fidelity. That assumes the A/D converter is properly dithered (as all modern converters are). That is my strong opinion, and I’m sure we can debate it right here on HRAC in the coming months. But does 44.1/16 really qualify as hi res?
By increasing those numbers, we increase the amount of information that is being captured. Increasing the sampling frequency increases the bandwidth of the audio signal; this increases the high-frequency limit of the recording. Increasing the number of bits increases the signal-to-error ratio; this in turn lowers the noise floor. It is the upmanship of these numbers where the concept of hi res audio is born. More specifically, a hi res audio recording attempts to go beyond typical fidelity by using signal capture methods that are beyond typical.
It’s also important to note that different technologies, rather than numbers per se, play an important role in audio fidelity. While PCM recordings can be undeniably good, there are options. Perhaps foremost is DSD coding used in the SACD format, a type of 1-bit coding appreciated by many audiophiles. Of course, perceptual coding methods such as ACC, as incredible as those algorithms are, do not qualify as hi-res.
Numbers aside, the improvements in signal capture with bigger numbers can be hard to quantify. For starters, if the recording is made in a studio with a relatively high noise floor, a 24-bit converter does indeed capture more information, but it’s just HVAC noise, so who cares? In other words, to take advantage of the higher numbers, everything involved in the making of the recordings must be at a much higher spec.
Then there’s the question of the audibility of the improvements provided by bigger numbers. A rigorous listening test conducted by Meyer and Moran (with the help of the Boston Audio Society) concluded that differences were not audible in a double-blind comparison of hi-res recordings versus 44.1/16. I did not take part in the test, nor have I carefully listened to the files it used, but I greatly respect its authors, as well as its methodology and conclusion. Those who are passionate about hi res audio must carefully temper their hot-headed enthusiasm with ice-cold science. You hear a lot of statements like “This 192/24 file blows away the CD” and “I can hear the difference in the other room” or “It’s obvious even with crappy earbuds.” These comments don’t really move the ball forward. My favorite is when someone compares a 192/24 file to a 44.1/16 file and they are completely different mixes. That also fails to advance our hi res team downfield.
So, what is hi res audio? There are at least two definitions. The first: A hi res recording is one made to specifications that are superior to 44.1/16. That’s well and good, but not particularly helpful. Specifically, as noted, when it comes to making a terrific recording, using big numbers is #1 on the List of Easy Things To Do. It’s everything else that comes later that determines whether or not the recording actually sounds good. Defining hi res audio by numbers alone is at best a joke, and at worst, a scam.
Now, don’t get me wrong. Although big numbers by themselves don’t impress me, I would still strongly prefer that engineers record with big numbers, and I prefer that I can buy those files with big numbers. It’s just that numbers alone don’t tell the whole story.
The second definition: A hi res recording is one that is made to specifications superior to 44.1/16 and is made with great concern for fidelity. Moreover, a hi res recording must sound better than most mass-market commercial recordings. The cause of the improvement in fidelity, big numbers or expertise — or both — is a question that probably still hasn’t been answered. To help clear that up, sooner or later, supporters of hi res audio will need to prove their contention that hi res audio can sound better because its numbers are bigger than non-hi-res audio.
So, again: What is hi res audio? Well, consider this: In 1964, the Supreme Court was wrestling with the problem of defining pornography. Not an easy thing. Beauty is in the eyes of the beholder. Famously, Justice Potter Stewart wrote that “hard-core pornography” is difficult to define, but “I know it when I see it.”
That kind of pragmatic judgment is exactly what we need when we deal with hi res audio. We don’t want to be pinned down by specific specs or formats. We want music that is recorded as well as modern technology permits, created by musicians, engineers, and producers who take the extra time and effort required to make the sound quality better than most other music out there. What is hi res audio? We’ll know it when we hear it. And we’ll be listening carefully.
Ken C. Pohlmann, a.k.a. The Professor, is a well-known audio educator, consultant, and author. He is professor emeritus at the University of Miami in Coral Gables, Florida, and is the author of numerous articles and books, including Principles of Digital Audio and Master Handbook of Acoustics.