Yes that's correct. I like a more revealing DAC - one that doesn't put a veil between me and those (same) digits.
Yes that's correct. I like a more revealing DAC - one that doesn't put a veil between me and those (same) digits.
In S-D DACs its noise modulation. In many R2R DACs, its glitching. That leaves a minority of multibit DACs to build revealing DACs with.
OK, Don. Opus is doing good, but you need to speak much.....more.....slowy.... And use smaller words. If you engineers want us to write the marketing copy for you, you have to give us language that we, and the reading audience, will understand. If you don't, being marketing guys, we'll just make something up, like, "the DonOpus Premier Ultra OneDac simply takes a deeper dive into the data on your disc or hard drive, extracting details that you never knew were there, that you've never heard before. But it accomplishes this Herculean feat without ever delivering that cold, etched hyper-detailed sound. It will transform your digital listening to one much more akin to SOTA analog. It will not sound like data playing through a system. It will sound like sweet, sweet music."
Tim VPBS, Marketing
Hand-waving again, hopefully not too techie but no promises...
DS DACs perform noise shaping and use high-order modulators, high clock rates, and lower-resolution "DACs" in a feedback loop to provide very low in-band noise. Noise shaping can provide very high in-band SNR at the cost of very high out-of-band noise. The noise rises with frequency, unlike conventional circuits that generally exhibit flat or falling noise floors with frequency (to a point well beyond the scope of this topic). Other issues DS DACs may have are that the modulators may be subject to strange spurious artifacts (noise/distortion tones) caused by the digital filters when certain combinations of signal and clock frequencies are hit. Perhaps the biggest advantage of DS DACs from an audiophile POV is that their very high sampling rate means the output filter all DACs require to reject out-of-band images generated by the sampling process can be placed at a very high frequency. That means less roll-off, phase shift, ringing and such is added to the audio signal by the filter.
Conventional DACs like R2R designs generate a glitch (like a noise spike) every time the data changes, and that glitch can be large (for an R2R, half full-scale). Worst-case, think of the MSB toggling: when the MSB turns on at mid-scale, all the other bits turn off, and a large glitch is generated. Since this is right at mid-scale, the glitch impacts low-level signals the most because mid-scale of the DAC is 0 V (the center) of a +/- output signal. This glitch generates signal-dependent distortion.
A conventional DAC that is not oversampled requires a steep filter at half the sampling rate to reject images that appear starting at and beyond half the sampling frequency. A high-order filter is needed, and that means (usually) a lot of phase shift, ringing, and roll-off extending well into the audio band. Conventional DACs can be oversampled, of course, to mitigate the filter effects. For that matter, you can oversample and filter to improve the SNR of a conventional DAC, but without the noise-shaping modulator the benefit is fairly small.
Sonically, noise shaping (DS) converters have a noise floor that rises with frequency and thus may be more audible/annoying in the highs, and added non-harmonic tones may corrupt the sound. The glitches and filters of conventional DACs can put an edge on the highs and smear transients, and their noise floor tends to have a "raspier" or harsher sound (though added noise to dither the lsb mitigates that in both architectures). The audibility of any of these effects is debatable, natch.
HTH - Don
Very, very, VERY cool! Thanks Opus! Appreciate your taking the time to share your experience.
What multibit DACs do you like?
And, as you would expect....what digital equipment currently uses them?
Can one 'sort of' generalize the sound of D S vs. R2R DAC's and if so what is generally the difference?
Simplified (and thus less precise):
Ideally, the distortion induced by jitter is dependent on the signal frequency, not the clock, so sampling rate does not matter (just resolution and signal frequency
That does not match my understanding of the DS transfer functions... The jitter requirement is based upon the aperture time, which in turn is related to signal frequency and resolution. The DS approach would be in serious trouble if the jitter was multipled by the over-sampling ratio (OSR) as you imply, unless I am not understanding your post (quite possible). See texts by Temes, Candy, and Norsworthy.
The high-frequency noise is much higher, true, reaching unity at Nyquist, the trade for suppressing the noise at low frequencies. However, that unity peak is reached at a frequency 64x the signal band (using your example) where it easier to filter. The total quantization noise energy is the same, but instead of being flat across the band, it is greatly reduced at LF and pushed into the HF side, well above the signal band.
I am not sure why the effect of jitter on noise matters? The noise, and HF jitter, is filtered out by the analog output filter (typically of order N+1 for an Nth-order modulator, but higher order is OK since the cutoff frequency can be well above the signal band.
A 2 MHz signal does indeed need 100x less jitter to provide the same resolution, but that is well outside the audio signal band.
There were a lot of arguments about noise and jitter, but empirical results showed it not to be any worse than "normal" DACs.
I thought Bob retired some time ago? I never met Dr. Hawksford.
Steve Williams Site Founder | Site Owner | Administrator | Ron Resnick Site Co-Owner | Administrator | Julian (The Fixer) Website Build | Marketing Managersing |