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Delta-sigma vs “Multibit”: what’s the big deal?

bennetng

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Yep, thanks for the ideas. I had thought of that too, zero order hold is basically what the iFi "bitperfect" stuff does, just hold the samples.
The result is similar enough I think :) but not 100%. Here is kitsune measurement from stereophile, seems a tad less noisy maybe.



The fun thing about the Kitsune is that you can exit out of NOS mode at the flick of a button :)
My screenshots are from a Realtek:p

The noise floor and spikes depend on the converter, they are not generated by the resampler. Without going through the analog chain it looks like this:

That means despite violating the sampling theorem, filterless DACs can still be objectively measured.
Image1.png
 

DonH56

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A number of RF systems use the images to produce direct-RF outputs. The main drawbacks are reduced output due t the sinx/x curve and subsequently greater noise. They don't technically "violate" the sampling theorem, it's just another application of it.

For audio, to apply that sort of ultrasonic energy to the rest of my system seems like a bad thing... But my hearing rolls off well below 60 kHz so maybe I just don't know what I am missing. :)
 

bennetng

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Chiptune synthesizers will not sound like chiptune synthesizers without severe imaging/aliasing.
 

AnalogSteph

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Speaking of chiptune, back in the mid-'90s you knew you had a fancy MOD player if it supported cubic spline interpolation in addition to 2nd-order and basic linear interpolation. It did make quite the difference in CPU usage, though I can't remember the specifics for the life of me.

A number of RF systems use the images to produce direct-RF outputs. The main drawbacks are reduced output due t the sinx/x curve and subsequently greater noise. They don't technically "violate" the sampling theorem, it's just another application of it.
It's called, guess what, a sampling mixer. You can do some neat things with these. A handful of essentially mechanically-tuned FM tuners used them to implement locking the LO to a fixed frequency grid of 100 or 50 kHz (made up by high multiples of fs = 100 / 50 kHz) instead of a traditional AFC. So you would get the frequency stability of a PLL-tuned set with the frontend selectivity of a mechanical varicap.

Stroboscopic speed indicators are another application of undersampling that may be a little closer to home for some. Here's the math if you're interested.
 

DonH56

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It's called, guess what, a sampling mixer. You can do some neat things with these. A handful of essentially mechanically-tuned FM tuners used them to implement locking the LO to a fixed frequency grid of 100 or 50 kHz (made up by high multiples of fs = 100 / 50 kHz) instead of a traditional AFC. So you would get the frequency stability of a PLL-tuned set with the frontend selectivity of a mechanical varicap.
I had not heard it called that but it's been a while. Another trick is to narrow the output pulses to be closer to an impulse than the typical ZOH stairsteps. You lose a lot of energy but the sinx/x rolloff is not such a big deal.

Technically, as long as the information bandwidth does not exceed Nyquist, you are not undersampling. It works for ADCs as well, with an appropriate (often gnarly) bandpass filter at the target RF center frequency and a sampling with sufficient bandwidth and low aperture error.
 

gvl

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I've been listening to multi-bit NOS DAC loan from my friend. A kitsune holo spring.

I have to say. I know this stuff measures worse, but I'm a sucker for NOS. I can listen for 7-8 hours without fatigue. Plus I don't hear the images/artifacting from not oversampling anyway. I really wanted to hate this thing..... :D it sounds great to me. The DX3 has more clarity but I get listening fatigue over time. The iFi black label had the same effortless fatigue-less sound but the holo spring is a much better DAC than the iFi.
I can definitely relate to this. I received my Khadas TB in December. I plugged it in, sat down, and flipped through a dozen tracks and it felt like "wow", I then disconnected the board and put it back in its box where it spent the next month sitting on a shelf. Only now I'm starting to take it in medicinal dozes with hopes my audio-sensory system will dull up a bit with use. Based on this experience I tend to think that a (really) well measuring DAC isn't necessarily a DAC for every occasion.
 

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