resolution magazine March 2014

TECHNOLOGY

The 1990s were exciting times for digital audio and digital audio convertor design in particular. Everything was new, challenging and promising. Sampling at 44.1kHz we were moving from zippery 16-bit, 18-bit, 20-bit and finally to smooth sounding 24-bit. Then there

was 96kHz, 192kHz and then in the early 2000s Sony brought the new great sounding 1-bit 2.8MHz DSD format. These were exciting times, full of experiments, discussion and controversy with numerous papers on the subject. Eventually, the SACD sound quality and excitement gave way to the practicality of the Itunes-Ipod mobile model. Quality recording took the back seat and in my world of digital audio design things seemed to plateau. The best convertors were now 24-bit, 192kHz with a maximum dynamic range of 120dB. Digital had matured with the performance good enough for the majority of the music world. But there were still a few of us working in the background pushing the envelope further, convinced that digital was still behind analogue.

I often look at the audiophile market for new ideas. These guys were not happy with Itunes sound and kept trying everything else. Vinyl and tape reissues continued to thrive and some time around 2007 the writing on the wall was clear: the internet was the future for all music.

The Itunes delivery model is about sound but we need more than the mp3. During conversations with Japanese DSD inventors we talked about the soon to come ‘Downloadable DSD’ file. Audiophiles love this format, revered as the holy grail, be it reality or perception. Soon files started popping up online. The pioneers were the tiny usual suspects: Blue Coast, Channel Classics, Linn, 2L, Opus3, Cybelle, David Elias Wheatus, and others, followed by dedicated download site services such as Hiresaudio.com, Prostudiomasters.com, Superhirez.com, Nativedsd.com, Onkyo.com and more (More detailed lists can be found at: http://www.audiostream.com/content/hd-music-download-sites)

In the PCM world the ambitious initiative of Music Giants download service was ahead of its time and closed in 2009. Soon after the Chesky brothers launched the most successful hi res music site, HDtracks.com while Itrax.com had offered 96/24 recordings for sometime. Today I can download a fantastic sounding recording in any format including 384kHz PCM, 5.1 surround DSD or 5.6MHz DSD, drag it into a playlist on my computer and playback through our Mytek Stereo192 DSD D-AC. I can hear the same exact native quality the mastering engineer heard when they finished the record. All elements are in place from recording to delivery, from studio to home. This year Mytek participated in the Hi Res Audio Showcase at CES in Las Vegas helping to raise consumer awareness while increasing demand to drive and challenge hi res digital audio production.

The DSD audio format has been a subject of controversy from the start. There were endless papers for and against it. Beloved by music lovers and hated by the traditional ‘in the box’ PCM production crowd. The format returned in-force with the advent of downloadable DSD. Lead by the likes of Mytek, Meitner, Playback Designs now almost every hifi D-AC today offers DSD playback. In my experience, every time we play a DSD recording, the magic of music returns.

Just as Photoshop can open jpeg, tiff, png or gif, the current computer playback chain is format agnostic. We can now playback mp3, .flac, 96k .wav and DSD .dsf files in the same playlist while one after the other each plays in its native format with no need to leave the couch.

In 2008 a new Company called ESSTech launched the 32-bit Sabre D-AC chipset aimed to push the performance envelope to 130dB DR and beyond. With an unorthodox architecture, this chipset quickly caught my interest. Eventually I met Sabre’s brilliant Canadian designers and learned more about their approach. It was clear 120dB DR and 24-bit was not the convertor design plateau any more. The new wave of very high performance chipsets was coming.

After incorporating the 32-bit (fixed-integer) chipset in our stereo 192-DSD D-AC we began our never-ending sound experiments with DSD and 32-bit PCM. This autumn we added a new 32-bit/DSD A-DC prototype circuit to the mix. Listening and measuring at our own mastering style Mytek R&D Studio in Brooklyn, it quickly became evident that with a very clean playback circuit of 130dB DR, very small differences do matter. It’s either more real, more analogue music or more grunge and veil. It was also apparent that the same hardware A-DC>D-AC chain is more transparent in DSD than in PCM.

DSD offered additional depth and resolution, although increasing the sample rate of 24-bit PCM to 192k brought the formats closer. 5.6 MHz DSD is better sounding still. We continued our experiments trying to understand if and when PCM can challenge DSD. While 384k brought the quality closer, it was not until we started toggling between 24 and 32-bit depth that we heard a major improvement. It was clear that in a clean digital chain with 130dB dynamic range, 24-bit, even dithered, is the bottleneck.

Further analysis of the architecture of modern A-DC and D-AC chipsets shows that 32-bit decimation output is the information subset of a very high performance quasi-DSD front end. This allows the capturing of another 48dB of additional detail depth. Going back to 24-bit decimation reduces detail. 32-bit is needed to clean up the modern high performance digital recording PCM chain. 32-bit at a minimum of 352.8kHz (DXD32) PCM would be needed to compete with DSD sound quality.

The next generation of PCM/DSD convertors from Mytek will have 32-bit integer output and at least 384kHz FS in addition to 11.2MHz DSD. Almost all current digital interfaces can only transfer 24-bit. The current AES-EBU and SPDIF digital audio interface is capable of 24bit, 192kHz only.

Fortunately with USB, Firewire, Thunderbolt and upcoming AVB network protocols, AES-EBU style streaming interfaces are becoming less relevant, as computer interfaces can shuffle any amounts of bits at any speed if programmed to do so. So despite most computer audio drivers being capable of transferring only 24-bit, they can be easily amended to feed 32-bit integer

Beyond 24-bitA cursory glance at technology’s progress would suggest that we’ve

plateaued at a comfortable level. MICHAL JUREWICZ, founder of convertor manufacturer Mytek Digital, suggests that the stakes are about

to be raised as he introduces the disruption of 32-bit.

Through the 90’s and beyond.

The Zeitgeist for Hi Res Audio.

DSD is here to stay.

32 bit sounds better than 24 bit.

Practical implementations.

March 2014 resolution

TECHNOLOGY

audio into 64-bit floating point OS environments. We are currently developing such an implementation for Mytek drivers and have begun collaborating with some high-end DAW software companies to implement it on the DAW side.

There are practical repercussions. With the advent of the downloadable hi res audio market, hi res digital music production not only results in better sounding records but it also makes economic sense. Currently the very same album can be offered for download for $10 for mp3, or $20 for 96/24 or $30 for the DSD version.

High resolution digital audio formats allow for greater resolution in recording, in turn this helps engineers to make better decisions in the recording chain from the microphone to the console. Thus an album requires less work and is more rewarding and easier to make. The results are much more satisfying and true to life. In addition, the distribution model that monetarily rewards quality is already in place and growing.

Numerous assumptions about subjective sound quality have been made and challenged in the past. General measurements of the human ear placing dynamic range at 120dB seem to refer to individual test tones rather than complex musical cues. It seems that increasing the resolution as much as possible retains sound quality better than rounding and dithering ever could. 2x and 4x DSD is an excellent format to achieve such results. Meanwhile a comparable PCM digital audio chain calls for 32-bit (integer) high speed conversion using a 64- bit (float) digital audio architecture.

FOOTNOTE:Michal Jurewicz graduated in EE from the Department of Electronics and Acoustics at Warsaw Technical University in 1987. After working as a technical engineer in New York’s Hit Factory and Skyline Studios, he founded Mytek Digital in 1992 in New York City. He has designed more than 30 digital audio convertors as well as other studio equipment.

Figure 1. Suggested High Resolution PCM Digital Audio Chain

Figure 2. Suggested High Resolution DSD (up to 4x speed) Digital Audio Chain

Practical repercussions.

Conclusion.