Great, succinct encapsulation.
https://www.schiit.com/products/yggdrasil
Unique True Multibitâ„¢ Performance
All Yggdrasil+ versions use our True Multibit architecture, a unique combination of our proprietary time- and frequency-domain optimized digital filter and integrated, medical/defense grade multibit D/A converters. Yggdrasil’s DSP-based digital filter has a closed-form solution—it retains the original samples, performing a true interpolation. Only this digital filter gives you the best of both NOS and upsampling designs.
Specs
Digital Filter: proprietary Schiit time- and frequency-domain optimized digital filter implemented on Analog Devices SHARC DSP processor
FAQ
What’s this bullschiit about a unique time- and frequency-domain optimized digital filter, and why does it matter?
Most digital filters destroy the original samples in the process of upsampling. They’re just like sample rate converters or delta-sigma DACs. We’re all about the original samples, so we created a unique digital filter that performs a true interpolation, which means it retains all the original samples. This is a major difference between Schiit True Multibit DACs like Yggdrasil and every other DAC in the world.
I don't believe you!
Then ask Mike Moffat, the father of audiophile digital playback, about his 5-year quest to perfect this digital filter, involving 1917 Western Electric papers on pulse-code modulation, a professor emeritus of mathematics who devised a way to get around the divide-by-zero problem, a RAND corp mathematician to implement it, and a master programmer to get it to run on our SHARC processor engine. In his words:
"The below are the claims of the digital filter/interpolator/sample rate converter in Yggy:
- The filter is absolutely proprietary.
- The development tools and coefficient calculator to derive the above filters are also proprietary.
- The math involved in developing the filter and calculating has a closed form solution. It is not an approximation, as all other filters I have studied (most, if not all of them). Therefore, all of the original samples are output. This could be referred to fairly as bit perfect; what comes in goes out.
- Oversimplified, however essentially correct: The filter is also time domain optimized which means the phase info in the original samples are averaged in the time domain with the filter generated interpolated samples to for corrected minimum phase shift as a function of frequency from DC to the percentage of nyquist - in our case .968. Time domain is well defined at DC - the playback device behaves as a window fan at DC - it either blows (in phase) or sucks (out). It is our time domain optimization that gives the uncanny sonic hologram. (It also allows the filter to disappear. Has to be heard to understand.) Since lower frequency wavelengths are measured in tens of feet, placement in image gets increasingly wrong as a function of decreasing frequency in non time domain optimized recordings - these keep the listener's ability to hear the venue - not to mention the sum of all of the phase errors in the microphones, mixing boards, eq, etc on the record side. An absolute phase switch is of little to no value in a non time domain optimized, stochastic time domain replay system. It makes a huge difference with an Yggy.
- This is combined with a frequency domain optimization which does not otherwise affect the phase optimization. The 0.968 of Nyquist also gives us a small advantage that none of the off-the shelf FIR filters (0.907) provide: frequency response out to 21.344KHz, 42.688KHz, 85.3776KHz, and 170.5772KHz bandwidth for native 1,2,4, and 8x 44.1KHz SR multiple recordings - the 48KHz table is 23.232, 46.464, 92.868, and 185.856KHz respectively for 1,2,4, and 8x. This was the portion of the filter that had the divide by zero problem which John Lediaev worked out, to combine with #4 above AND retain the original samples.
This is what other DACs typically offer: frequency domain optimization FIR filters with Parks-McClellan optimization. Any avoidance of the Parks-McClellan pablum requires a lot of original DSP work. Am I a prophet who received the tablets from God or some other high-end audio drivel. Hell, no. I was the producer and director of this project and worked with Dave Kerstetter (hardware-software), John Lediaev (Math), Tom Lippiat (DSP Code), Warren Goldman (Coefficient Generator and development tools) for a total of 15 or so man years. These folks either taught math at The University of Iowa, Computer Science at Carnegie-Mellon University, worked at think tanks like the Rand Corporation – you get the idea. We did this for no money - What we all had in common was that we loved audio. All other audio pros were interested in Parks-McClellan and pointed and laughed at us. That's the way it happened. It was worth it, every hour, day, and year."
