The Resolution Revolution

By Roger Nichols

Sept-2003

There are literally dozens of surround DVDs being introduced every month. The reviews talk about the higher resolution of the DVD-A and DSD audio releases. Yes, it is great to have 96k/24bit audio to playback on your high-end audio system, but it seems curious that the resolution of the final product is much higher than the original recordings.

Remember when CDs first appeared? There was a rating system in place that told you the evolution of the recording. The three stages of the recording were; 1) the multi-track tape format, 2) the mix-down format, and 3) the mastering method. “A” was for analog and “D” was for digital. If a CD was rated D-D-D it meant that the multi-track tape was digital, the mix-down tape was digital, and mastering was digital. For marketing reasons the record companies wanted as many Ds as possible. Even though the third D was supposed to tell you whether the CD was mastered in the analog or digital domain, the record company always used a D because “The final step was digital because the end result is a CD.” The rating system was finally dropped because it was completely up to the artist and the record company, and there was no way to tell when a stage was analog or digital.

Now that we have DVD-A we are again looking at the marketing departments and not the technical departments to tell us what is on the DVD-A. When you read the back of the DVD-A and it says that the album is presented in 96k/24bit you would assume that it was recorded in this higher resolution. This is not always the case.

As an example, let’s say that you have a multi-track digital tape that was originally recorded at 48k/16bit. You mix the album through an analog console and print the mixes to a piece of analog tape. The analog tape then goes to the mastering house and the mastering is done at 96k/24bit. Where did the extra resolution come from?

Ok, for a second let’s ignore the analog tape. When you EQ or compress or otherwise process a 16bit signal, there are products generated that can only be captured by a greater bit depth. If you lower the level by 0.1dB the results can only be accurately captured at the higher 24bit resolution. If you print the mix to analog tape, there are artifacts such as harmonic distortion, wow, and flutter that can be better captured by a 24bit conversion.

I have a problem in two areas. The first area is mastering a 48k source at the higher 96k or 192k sample rates. There is no new information generated that has anything to do with the original material that would require the higher 96k or 192k sample rate.

The second problem is the act of printing the mix to analog tape for the purpose of retrieving the mix from that tape at a later date for re-release at a higher sample rate. This problem has actually two sub-problems. First, the mix, after being printed to analog tape contains the additional artifacts, as stated above, that are not part of the mix. These artifacts are distortion. Any additional information that is not part of the original information is called distortion. This includes clipping, compression, wow, flutter, tape non-linearity, phase shift, cross talk, and harmonic distortion caused by the tape medium. Second, the audio content of analog tape changes over time. The mix will not be the same in one year, one month, or even one week. If the mix is re-sampled at a later time, even at the same sample rate, there will be a difference in sound because of the deterioration of the magnetic recording.

Reviews in high-end audio magazines praise the fact that there may be a later transfer from the analog mixes of the album at a future higher sample rate. This, of course, is for even more enjoyment when consumers are afforded the next generation of audio playback units. The quality won’t be better, it will in fact be worse, mostly because of time passed and the generation loss caused by the analog tape.

The higher resolution product will definitely sound different, but maybe this is all the public wants. Maybe they just want to own every permutation of the sonic possibilities.

When CDs were first released, there were some complaints that CDs did not sound as good as the vinyl albums they would eventually replace. After some investigation it turned out that the vinyl records were mastered from the original analog or digital master tape. The first-generation, original master mix tape. The CD was made from a second-generation analog tape copy. Yes, an analog tape copy was sent to the CD plant. Artists and producers yelled and screamed and the mistake was corrected.

The same thing is happening to the audio on DVD-A and DSD releases. What you think you see is not really what you get. The 44.1k/16bit CD is made from the original master tape. The DVD-A is being made from an analog copy, even if it is a 96k/24bit high-resolution disc; it is still made from a copy. At over $20 each, we are surely not getting what we paid for.