(Ed. note: Enjoythemusic.com has just published the summary of an intriguing investigation into whether there are audible differences between uncompressed WAV files and lossless FLAC files. Links to the full study can be seen at that site.)
In a previous four-part series on computer audio sound quality (The Absolute Sound, issues 218-221), we examined and ranked a number of hardware and software factors that affected ripping, burning, and playback sound quality, using standard PC-based computers. These articles defined several industry-standard criteria on which subjective judgments were based. And in order to provide a measure of the magnitude of these effects in such a way that readers could understand and reproduce in their own systems, we created a numerical scale based on subjective estimates of the fractional difference between the sound of a CD, of a SACD, or of a high resolution download derived from the same master recording.
Part three reported that a FLAC file sounded inferior to the WAV file from which it was made, and we found to our surprise that when these FLAC files were reconverted, the resulting WAV file did not recover the full sound quality of the original. We repeated these conversion steps five times and observed a hyperbolic decline in WAV sound quality, the greatest loss occurring in the first two or three conversions.
To avoid inevitable controversy, these experiments were repeated several times, using a single blind protocol with various trained listeners, and consistently obtained the same results. Since the FLAC compression is considered lossless, it was no surprise to find considerable objections posted on the ‘bits are bits’ forums when we published. The validity of our results was recently questioned again, so we reexamined our original findings, partly in an attempt to understand the cause, but also using updated computers, software, DACs, cables and other system improvements (see TAS issues 246 and 248). The results of these reinvestigations are the subject of this summary article, and the reader is referred to the full two-part article available as a free download at www.hificritic.com/flac_wav_sound_quality.
The equipment and a detailed methodology are described in the abovementioned download, and in TAS issue 246. The latter describes the serendipitous discovery that a single measurement of the height of specific instruments (in the few recordings where such information was captured) correlated with our listening criteria. Height could therefore act as a legitimate and quantitatively accurate proxy for subjective sound quality judgments, an approach that allowed rapid repetitive and time-independent measurements made weeks apart. In addition, this technique allows for significant statistical analysis between the relatively small perceived height differences associated with subtle sound quality changes.
Presentation Of Data And Results
The basic protocol used in most of the experiments in this article is as follows. The original recording used in these experiments was obtained from an Acousence DVD-R ACO-DF 41610, by copying a 24-bit/192kHz FLAC file of Chabrier’s Espaato the computer hard drive. This file was then converted to WAV format then back to FLAC using dBpoweramp (dBPA) v14.1. This was repeated 5 times sequentially to obtain what we have designated as FLAC 0, WAV 0, FLAC 1, WAV 1 through to FLAC 5 and WAV 5.