Which S-D chips these days use PWM? I haven't seen any myself. Sabre doesn't, to my knowledge. I
think the new NAD being talked about here might use PWM.
Apologies, I should have wrote PDM. Late night - and a few beers
When I say multibit I mean a DAC which hasn't used noise shaping and truncation. So even the venerable
TDA1540 counts as multibit (despite being just 14bits) whereas Sabre (which uses 6) does not. So the distinction
does remain clear to me at least.
Yes I understand where you are coming from and there are many with your perspective on this.http://www.esstech.com/PDF/sabrewp.pdf
However from the white paper and from discussions at DIA, with Dustin Formin one of the designers, they have put
a huge amount of effort in overcoming traditional problems with the modulators. For example noise floor modulation
The biggest frustration with Sabre for me is they dumped an ASRC in the chip aswell. I would have loved to see that as
a separate chip and keep the DAC as simple as possible. Apparently they did consider this.
Agreed - Sabre almost guarantees the designer will need a groundplane. With TDA1541 this isn't essential. So
how do high speed decoupling requirements translate down to audio?
This is the million dollar question. Objectively or subjectively??
I know what works and sounds good subjectively, I know what is the correct way to do the design from an RF design perspective,
Somewhere in between is the answer. This is the problem of audio.
If, as SteveN implies its about keeping the supply series impedance flat across the audio range then how is this affected by the impedance presented to the
DAC chip at RF?
I don't know that Steve was implying this. But they are separate issues, power supplies for opamps and in the Sabres case supplies for
analog OP stage, digital stages etc. Personally I would treat them differently.
Ah, we differ on whether 'musical' and 'accurate' are polar opposites. To me they're definitely not. Transparent to me means accurate
and transparent to my ears is also musical.
Yes, if you look throujgh this forum and all others you will find years of 'colorful discussion' on this subject.
I used to have exactly your view for many years. However these days, after many years of building stuff for recording and playback
I have changed my views to a certain degree. Your view applies to a perfect world with pefect studios and perfect playback.
I haven't found that perfect world yet. In my engineering heart I think -exactly- like you do. Unfortunately the reality of life's
experience has been different and this conflict has many times made me even want to give up audio design altogether.
Having a larger I/V resistor will tend to increase the low order distortion (2nd mainly).
Its not true (from the DACs I've examined) that multibit in general has a more benign THD profile - take a look at the recent review by
Colloms of the Metrum DAC as an example - I've never seen an S-D looking quite as aggressive as that.
Haven't seen the review or measurements. In fact does anyone know what DAC they are using?
I was referring to R2R dacs like PCM63/1704 etc that always have increased low order distrtion with OP voltage swing.
Subjectively they sound richer / less precise with more voltage swing.
+1 for Samuel's paper. Very informative. But in my experience not that relevant to sound quality which isn't really strongly correlated
with those measurements.
IMO, read between the lines so to speak and look at common mode distortions and OP loading distortions. These accoun for a
lot of the sound of an opamp.