High resolution (Hi-Res) audio is not as good it should be, causing an industry group to create new production guidelines to address what it says are "misperceptions" concerning what it takes to create the best recordings.
The guidelines will come from the Producers and Engineers wing of the Recording Academy, the organisation behind the Grammy awards. The initiative was announced yesterday in New York City, at the CE Week event.
Hi-Res audio (HRA) is an effort to stimulate interest in high-end audio by promoting recordings and audio systems that are better than CD quality.
At last year’s CE Week, the Digital Entertainment Group, a non-profit advocacy group for the entertainment industry, announced a formal definition of HRA in association with other industry groups as well as Sony, Universal and Warner.
According to this, it is “lossless audio that is capable of reproducing the full range of sound from recordings that have been mastered from better than CD quality music sources.”
"Today, listeners can hear the music in their home exactly like we do in the studio when we record and mix it," said recording engineer and mixer Frank Filipetti.
The most common digital encoding system, called PCM (Pulse-Code Modulation), has a resolution defined by its sampling rate (how many times per second the audio is sampled) and its bit depth (the accuracy of the sample).
CD quality (16/44) has a 16-bit depth and a 44.1 kHz sampling rate. Common HRA resolutions are 24/96 or 24/192. Another encoding system used in HRA is DSD (Direct Stream Digital) as found in SACD, a one-bit system which uses a very high sampling rate of 2.8 MHz or more.
There is no consensus on how much is enough. Increasing the sampling rate extends the frequency response, while increasing the bit depth lowers the noise floor, improving the dynamic range; that is, the difference between the loudest and quietest sounds that can be reproduced.
CD quality offers a theoretical frequency response up to 22 kHz and a dynamic range of up to 96 dB, which is more than sufficient for human hearing at normal playback levels. Nor should you be deceived by graphs showing stair-step sound waves; the Nyquist-Shannon sampling theorem proves that a bandwidth-limited wave can be perfectly captured and reconstructed to be as smooth as the original.
Real-world implementations may not live up to the theory, of course, and audiophiles point to things like the impact of frequency filters (necessary for digital conversion) or the subtle effects of hypersonic sound (above the range of human hearing) on musical enjoyment.
Even so, while there is plenty of subjective evidence from audio enthusiasts who love their hi-res music, efforts to demonstrate the audibility of HRA over CD quality though scientific listening tests have been generally negative or inconclusive.
The UK Advertising Standards Authority rapped Sony last year for its stair-step graphs, commenting: “Whilst we acknowledged that the technology used in HRA allowed more data to be captured and greater frequency range and wider dynamic range reproduced, we had not been provided with any evidence that the differences were perceptible by the average person.”
It would be a brave person who said that HRA has no audible benefits whatsoever but it is hard to argue that those benefits, if they exist, are other than subtle. This is a challenge for HRA advocates, since unlike, say, high resolution video, it is hard for most people to discern a difference.