Popular Post Miska Posted July 20, 2021 Popular Post Share Posted July 20, 2021 2 hours ago, GoldenOne said: Some other dacs like some of the teac and ifi dacs have a 'pseudo-NOS' option made possible by the architecture of the burr-brown chip it seems. Though it's not actually NOS all the way through. The top 6 bits are though. Others like the ADI-2 and more recent AKM dacs have a 'super slow' filter which is basically a zero-order-hold OS filter. Still OS, but produces a result very similar to actual NOS. "NOS" in these cases means it bypasses the 8x digital filter, and just leaves the zero-order-hold OS in place. Same for TI and AKM. DAC chips just don't have enough DSP power to run proper 256x or higher digital filters, so they typically have digital filter up to 352.8/384k rate and rest is just OS by copying same sample N times. However, TI chips pass DSD inputs straight to analog FIR conversion stage and now AKM chips have similar feature feeding DSD data straight to their SCF conversion stage. So DSD inputs can be true NOS. This allows running proper 256x or higher digital filters and high quality modulators not constrained by the on-chip DSP. orosie, The Computer Audiophile, semente and 1 other 3 1 Signalyst - Developer of HQPlayer Pulse & Fidelity - Software Defined Amplifiers Link to comment
Miska Posted July 20, 2021 Share Posted July 20, 2021 12 minutes ago, GoldenOne said: The weird thing with the ti/bb chips though is that they show different results when you feed it 44.1khz content and use the 'nos/bitperfect' mode, vs using zero-order hold upsampling to 768khz etc and then feeding that to the dac. Not sure why Because they are not designed to be used in that way. That "NOS/bitperfect" mode is "external digital filter mode". And they assume to be receiving 705.6/768k input instead of 44.1k. If you still send them 44.1k, they are running whole thing at 16x lower rate than designed. Superdad 1 Signalyst - Developer of HQPlayer Pulse & Fidelity - Software Defined Amplifiers Link to comment
Popular Post Miska Posted July 21, 2021 Popular Post Share Posted July 21, 2021 10 hours ago, GoldenOne said: But if its doing zoh internally why does it behave differently when fed zoh externally? Is the modulator itself running slower? Yes, it is, because the entire thing is running slower. ZOH / S/H factor is static in that case. Or semi-static, since TI chips have three configurable ZOH / S/H factors, you just cannot exceed maximum output rates, but these are to accommodate 8x / 16x digital filter rates. Since their (TI and AKM) internal filter can go to max 8x while they support external filters that can go up to either 8x or 16x. 8 hours ago, GoldenOne said: The most similar filter would probably be something like poly-sinc-short-mp I'd guess though @Miska is the one to ask. I'm not sure HQP has any filters that short as it kinda goes against the point of having HQP in the first place. poly-sinc-short-mp is more like some DAC chip minimum-phase filter, but with the difference that it has >192 dB stop-band attenuation and thus reconstruction accuracy to 32-bit level. polynomial "filters" (interpolators) are closest to "NOS" with least filtering efficiency, then a somewhat longer is minringFIR. semente, GoldenOne and Superdad 2 1 Signalyst - Developer of HQPlayer Pulse & Fidelity - Software Defined Amplifiers Link to comment
Miska Posted July 26, 2021 Share Posted July 26, 2021 28 minutes ago, idiot_savant said: This is interesting - do they adjust the analogue filter for the various DSD rates? Usually more than PCM DACs do. Since typical DSD conversion section is clock rate dependent analog filter. Whereas PCM conversion section doesn't include filtering. Then typically in either case, following the conversion section is normal analog low-pass filter. Signalyst - Developer of HQPlayer Pulse & Fidelity - Software Defined Amplifiers Link to comment
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