[Jawed]

This paper:

UNDERSTANDING SIGMA–DELTA MODULATION: The Solved and Unsolved Issues

provides a nice summary:

• limit cycles
• idle tones
• harmonic distortion
• noise modulation
• deadzones
• instability

These problems apply in varying degrees whether the modulator is single- or multi-bit.

Other stuff I found:

GLOBAL STABILITY, LIMIT CYCLES AND CHAOTIC BEHAVIORS OF SECOND ORDER INTERPOLATIVE SIGMA DELTA MODULATORS

which proposes a bandbass sigma-delta modulator that's "tuned" for improved stability and signal to noise ratio.

And:

Frequency Domain Min-Max Optimization of Noise-Shaping Delta-Sigma Modulators

which is a technique for deriving the optimal bandpass modulator.

 

[goodvibes]

A bit old and things move forward but is a good example of not knowing what we don't know as VG engineers realize is the often the case. I understand the need for answers and a desire to limit subjective observation but there's always more than wrote #s. Sometimes we're not measuring the right things or have even discovered what to measure.

 

[bigshot]

That is probably more true in recent technology, but not so true for perceptual things and the physics of sound. Those things have been studied and understood for over a century. If humans can hear it, it's a safe bet that scientists are already measuring it.

 

[spruce music]

Another link to read the paper.

https://pdfs.semanticscholar.org/efc2/559deb5f3b4b7251182ddb2f087350abb661.pdf

 

[Jawed]

What I find interesting with this research is that some of these problems just aren't fully understood. It's a bit like the way "chaos theory just comes along from time to time and makes something you thought was simple behave in a way that is not simple".

Now playing: Charlie Parker - How Deep is the Ocean

 

[castleofargh]

you have to consider that when they admit to something not being fully explained, sometimes it really just means that nobody went to research that specific aspect yet, so nobody dares to claim anything. other times it can mean that we have a working model between action and reaction, but we don't necessarily understand why(like gravity). the element of mystery does not necessarily lead to chaotic results. in fact sigma delta is one of the those designs where theoretical and practical results come to be impressively close to one another. it's not something we could say about R2R designs, even if the limitations are clearly on the manufacturing side for that one.