Encapsulation and Musical Origami
Now we have an extremely high-resolution file (by virtue of the reduced temporal blur, advanced sampling and quantization methods, and other techniques) with a much smaller file size than one generated by 192/24 encoding. How can that file be compatible across all playback platforms, from a 44.kHz/16-bit smartphone to a state-of-the-art, five-figure, high-resolution DAC at the front end of a reference-grade home system?
The answer is in the technique Meridian calls “Encapsulation.” Look at Fig. 7, the coding space of 192/24 with the triangle superimposed in orange over the Ravel quartet we saw in Fig. 4. The red line is the music signal’s peak spectral content, the blue line the recording’s noise floor. The enclosed area within the orange triangle is equivalent to 900kbps peak/channel (around 900kbps average for two channels). Encapsulation captures and protects this region. Incidentally, you can see from this illustration that if we have to reduce the coding area to one-eighth (to fit two channels into MP3 or AAC at 192kbps), a lot of the music inside the triangle would be removed.
The signal space is divided into three areas: A is the frequency band up to 24kHz, B spans 24 to 48kHz, and C is information and noise from 48 to 96kHz. Above 55kHz, the signal has fallen below the background noise, so C is mostly an artifact of the original sampling or recording system—the paradox I referred to earlier.
Encapsulation takes the information within the triangle that falls within Area C and “hides” it beneath the noise floor of the recording in Area B. So any information we care about that was within Area C (within the small point of the triangle that protrudes into Area C) is now encoded and buried beneath the noise floor in Area B.
Taking this concept a step further, audio signals within the triangle of “B” (audio frequencies from 24 to 48kHz) are encoded and losslessly buried beneath the noise floor, but underneath Area A and along with C, as shown in Fig. 8.
Fig. 9 shows the final result of Encapsulation with the components of the signal above 24kHz buried within the standard-resolution signal. The resulting file contains all the information that matters—and none that doesn’t. In fact the lossless burying is even cleverer than the illustration indicates because it provides multiple replay compatibility and streaming options. This file can be formatted as FLAC or Apple Lossless. If you play it on a DAC that lacks an MQA decoder, you’ll hear the information in Area A with better-than-CD-quality and no loss of fidelity from the presence of B or C.
But if you have an MQA decoder, the decoder will “unfold” the hidden information (Areas B and C) in two (or more) steps, to produce a high-resolution bitstream with all the information that had been inside the triangle of the high-resolution original (Figs. 10 and 11). Meridian calls this unfolding “Music Origami.” The music can be enjoyed by legacy listeners at each hierarchical step. Fig. 12 shows the fully unfolded signal with the system’s end-to-end frequency response and time behavior (low temporal blur) in the box at the top right.
As a final reflection, Bob Stuart told me that the real target is to have a coding system that does no more damage than air. Air is analog; it’s never lossless, but it is as transparent as we can get. In coding terms he equates it to an infinite sample rate, but with an 18-bit noise-floor. Actually ten meters of air introduce more temporal blur than the complete MQA encoding/decoding system, as seen in Fig. 11—a tantalizing prospect to say the least.
MQA accomplishes the seemingly impossible—delivering extraordinary sound quality in a form that easily integrates into the existing music distribution infrastructure, is backward compatible with existing hardware, and serves all applications, from smartphone streaming to high-end home downloads, with a single file. The combination of streaming—which is poised to become the dominant paradigm—and MQA could usher in a world in which the term “high-resolution audio” is as anachronistic as “digital camera” or “flat-panel television.” All music will be high-resolution.