Audirvana Plus 3 for Windows (Official Thread)

[Miska]

Edit: Wrong thread...

[Miska]

Multi-level SDM is not the same as PCM. (And if you want, you can also upsample 1-bit DSD as is.)

 

Note that multi-level SDM can typically have for example 3 or 5 levels that doesn't match with any number of two's complement PCM bits. For example modulators in TI DAC chips have 5-level output, that is log2(5) = 2.3219 two's complement bits. Advantage of  multi-level SDM compared to PCM is that for all values except 0 and maximum, multi-level SDM has more than one representation for the same value. This is one property that multi-level SDM DAC chips extensively utilize. Same feature allows also good quality bit-perfect DSD conversion when used correctly.

 

6 hours ago, jamesg11 said:

As with what Miska does in HQP?

 

HQPlayer has two modulator variants, one that eats PCM inputs and another that eats SDM inputs (2 - 256 level). To be exact, there are two totally separate DSP engines, one for PCM outputs and another one for SDM outputs since these work in a different way. The SDM input one can remodulate directly from one SDM rate and number of levels to another SDM rate and number of levels. So for example rate is converted directly from 2.8 MHz to 11.3 MHz, without any intermediate rate. The modulator itself has gain property which allows adjusting volume as part of the process. You can also bake other kind of things into the modulator.

 

Also things like convolution are processed at the native rate, so for example if you do convolution for DSD256, it is processed at 11.3 MHz sampling rate.

 

5 hours ago, Jud said:

DSD, strictly defined, is 1-bit.  It's PDM or PWM, not PCM.  Anything with more than 1 bit has a PCM component.

 

So you define 2-level SDM very strictly and PCM very loosely.  If you are that loose, you can also say that DSD is just 1-bit PCM. Much simpler to call everything PCM! It would be better to be equally strict on both.

 

Equally strictly defined, PCM is two's complement (binary encoded) integer representation. So either DSD is also PCM, or HQPlayer doesn't convert to PCM.

 

 

[Miska]

41 minutes ago, Jud said:

My notion of DSD is that it's 1-bit, with values obtained through pulse width/density (more 1s for higher values, more 0s for lower values), like adjustments to a steering wheel, whereas PCM "words" have assigned values like points on a graph or map, and bits within the "word" have different values depending on position, so 010 and 100 are different.

 

There can be smaller and larger pulses. Good example being DSC-1 DAC where after each bit the conversion output can have one of the 33 possible values. Yet it is totally bit-perfect DSD converter.

 

And you can have for example 1-bit word with values 0 and 1. And you can have 32-bit word with values 0 and 1. Both have same meaning. Or you can have letter 'a' and 'b' instead. So it won't make any difference. So in your generalization, then also DSD would be PCM.

 

41 minutes ago, Jud said:

bits within the "word" have different values depending on position, so 010 and 100 are different

 

That is not the case for multi-level SDM. You can also interchangeably transform between the two representations, to limited extent.

 

41 minutes ago, Jud said:

I thought I recalled something different from a conversation between you and mansr here on the forums, but I could be misremembering.

 

Can you give a pointer?

[Miska]

6 minutes ago, Jud said:

 

Wish I could! I would have to search, and if I am misremembering, I wouldn't find anything.   

 

The Wikipedia article gives a nice outline of the picture I have in my head (in the "DSD technique" section), as well as saying things are really more complex than that, especially these days.  https://en.wikipedia.org/wiki/Direct_Stream_Digital

 

 

That is quite a bit of simplification. And I don't think it makes sense to attempt cover all the details in Wikipedia or forum post. There are books and research papers about SDM stuff, because it is so widely on A/D and D/A converters these days. Lot of companies don't tell much details how their chips work either.