By John Siau
November 29, 2013
What constitutes “High Resolution”? In the realm of video media, High Resolution or High Definition (HD) is pretty clear. The difference is clear between the old 4:3 standard-definition televisions and newer 1080p HD televisions. And if you’ve ever seen a 4k television compared to a 1080p set, well, the difference there is even more visible. It’s right there in front of your eyes.
While showrooms can really show off High Resolution video, that isn’t always the case with high-definition audio. There are a couple reasons for this, which we’ll get into in a later post. Also, we thought it would be a good idea to introduce the value of High Resolution audio. Almost everyone these days is acquainted with HD televisions. In contrast, it seems like relatively low-quality quality audio media – or even lower-quality streaming options like Spotify and YouTube – predominate in popular audio.
To start, let’s walk through the basic way in which a musical recording reaches your living room.
Say you’re listening to a four-piece rock band. They’ll record several tracks in the studio – that is, multiple guitars, drums, vocals, etc. – to a digital or analog source. It’s not especially important which. At that point, the audio quality is extremely high in order to give audio engineers enough headroom to make adjustments to the recording during mixing and mastering. To use a visual metaphor again, it’s like the studio takes a very high-quality (high resolution) photograph of a scene in order to make a fairly high-quality zoomed-in and cropped version for you to look at. When the whole process is finished, what exists are the “studio masters” of the final songs on an album.
These masters can then be transferred to a physical medium: a vinyl record, a CD, a cassette tape, and so on. Each of these media has some strengths and weaknesses, obviously. In the world of hi-fi audio, it’s pretty acceptable to believe that your overall experience is only as good as the weakest part of your entire set-up. To dip back into the visual realm: if you watch Casablanca on a 90 inch HD television, it will still look pretty crummy if your source is an old, beaten-up VHS copy from the library. You would prefer a masterfully restored, Blu-Ray source. Hi-fi audio is no different.
High Resolution audio has existed in some form or other for quite a while. Reel-to-reel tape players were de rigueur in the audiophile community throughout the 60s, 70s, and 80s. Later on, compact discs were seen as a high-quality audio source. In 1999, Sony and Philips introduced the Super Audio CD (DSD). An SACD holds about as much digital information as a DVD, which allows for the audio files it plays to be larger, thus containing more detail about how a recording sounds. A year later, DVD-A (PCM) entered the market, offering an even higher resolution than SACD. With all digital audio (CDs, SACDs, DVD-A, MP3s, and so on), the quality of a recording is directly dependent on how much information it holds. Thus, larger-sized files generally equate to higher-quality audio.
For a long time, digital audio has had a bad name because of the low quality of early MP3s. A lot has changed since Napster, though. Back then, files were downloaded over dial-up Internet. The computer technology used to compress digital audio files from CD-quality to MP3-quality was more primitive than it is today. Over 37% of all music album sales are digital; it’s not going anywhere. And that’s a good thing! Nowadays, a 320 kbps (that is, 320 kilobytes of audio information per second – a unit of measurement) is virtually indistinguishable from a CD by untrained ears and/or on low-end equipment. Audiophiles, though, possess far from untrained ears and much better than low-end equipment.
Enter High Resolution audio, again.
Services like Bowers & Wilkins Society of Sound; Blue Coast Records; eClassical;High Definition Tape Transfers; High Res Audio; HDtracks; Unipheye Music; and many, many more offer the digital audiophile HD audio he can download in an instant.
High Resolution audio differs from simple “lossless” digital music such as WAV, FLAC, and Apple Lossless files. While High Resolution audio may come in one of these lossless formats, not all lossless format audio is High Resolution. Lossless simply means “not compressed”, but the thing that is not compressed could be a standard-definition audio file – from a CD for instance. You could have a lossless version of a song from a CD and a lossless version of a song from an DVD-A, and the latter would more arguably be High Resolution.
That distinction goes a long way toward, finally, explaining what High Resolution audio really is. High Resolution audio files generally come in 24-bit/96kHz quality, which has twice the bandwidth of a CD (at 9612 kbps, or about 30x the quality of the “virtually indistinguishable” from a CD 320 kbps file mentioned above). The 16-bit quantization noise on a CD is audible at high playback levels; the quantization noise of a 24-bit playback system will always be well below the threshold of hearing. By design, CD audio (roughly meaning, consumer-level audio) approximates our sense of hearing. High Resolution 24-bit/96kHz audio files are designed to exceed the capabilities of our hearing in all respects.
With their extremely high bandwidth, High Resolution audio files are on par with the studio masters of a recording. One issue that can muddy the water is that sometimes the studio masters are not very good (for very old recordings, for instance) or the files are from masters, but not the original studio masters.
According to Dr. Mark Waldrep, CEO of AIX Records, a good definition of HD audio is:
"A recording that has been captured during an original session using equipment capable of matching or exceeding the capabilities of human hearing. If the generally accepted measure of the human auditory system includes a frequency span of roughly 20 Hz to 20 kHz and a dynamic range that tops out at around 135 db, then a recording system would need to be able reach these specifications to be considered HD. In the world of PCM digital recording this would translate to 48 kHz and 24-bits. Given there is some evidence that higher frequencies may impact our listening, moving to 96 kHz has some advantages for equipment designers and music fans. As an engineer, I choose 96 kHz/24-bits as the minimal specifications to achieve HD-Audio."
It’s entirely possible to create an audio file that is technically 24-bit/96kHz quality, but it could be a 24-bit/96kHz quality version of a poor recording. Once more to the visual: a pristine, high-definition film print of a movie made on a home video camera will not look very good.
Hopefully this rather long introduction hasn’t either bored you to tears or warned you off high-definition audio altogether. High Resolution audio is one of the greatest things ever to happen to audiophiles. As we continue talking about High Resolution audio a little later on, we’ll get into the more technical aspects of why that’s the case and what you can expect from a proper High Resolution home audio system.