On 10/18/2012 12:34 PM, Robert Adams wrote: > Another reason to keep those bits is that there is often a digital > volume control in the Codec, so you would like to be able to turn > down the amplitude by 20 db or so without losing any of your dynamic > range. Analog volume controls are becoming a thing of the past. The digital volume controls I knew were four-quadrant DACs with another DAC setting the reference voltage. (Analog Devices made some with a log-taper control DAC.) What is the modern practice? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Why there are so many bits in sigma-delta audio codec?
Started by ●October 18, 2012
Reply by ●October 19, 20122012-10-19
Reply by ●October 19, 20122012-10-19
On 10/18/12 11:48 PM, Jerry Avins wrote:> > On 10/18/2012 12:34 PM, Robert Adams wrote: > > Another reason to keep those bits is that there is often a digital > > volume control in the Codec, so you would like to be able to turn > > down the amplitude by 20 db or so without losing any of your dynamic > > range. Analog volume controls are becoming a thing of the past. > > The digital volume controls I knew were four-quadrant DACs with another > DAC setting the reference voltage. (Analog Devices made some with a > log-taper control DAC.) What is the modern practice? >i think it's a single 2-quadrant DAC with a bipolar reference voltage. like an R-2R network. the audio gets connected to the reference voltage input and the digital word is the gain. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●October 19, 20122012-10-19
rickman <gnuarm@gmail.com> writes:> On 10/18/2012 8:04 AM, Randy Yates wrote: >> Robert Adams<robert.adams@analog.com> writes: >> >>> In a sigma delta ADC, >> >> and by the way, it's "delta sigma"! > > > As long as you want to nitpick, (or is it nitpik?) the last time I > looked it up (I can't keep the order straight) they said it was > acceptable either way. I don't recall who that was, but I don't think > it was Wikipedia, rather someone a bit more authoritative.Rick, Oh sure. This is a long-standing joke between me and comp.dsp, although I may be the only one who finds it funny... -- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com
Reply by ●October 19, 20122012-10-19
On 10/18/2012 9:43 PM, Les Cargill wrote:> Robert Adams wrote: >> Another reason to keep those bits is that there is often a digital >> volume control in the Codec, so you would like to be able to turn >> down the amplitude by 20 db or so without losing any of your dynamic >> range. Analog volume controls are becoming a thing of the past. >> >> >> Bob >> > > The volume control in the codec should be using floats for > math - no raise of the noise floor if you do it right.At some point you have to turn the number back into a fixed for output to the DAC. At that point a reduced audio level will result in a lower signal to noise level. Rick
Reply by ●October 19, 20122012-10-19
On 10/19/2012 9:37 AM, Randy Yates wrote:> rickman<gnuarm@gmail.com> writes: > >> On 10/18/2012 8:04 AM, Randy Yates wrote: >>> Robert Adams<robert.adams@analog.com> writes: >>> >>>> In a sigma delta ADC, >>> >>> and by the way, it's "delta sigma"! >> >> >> As long as you want to nitpick, (or is it nitpik?) the last time I >> looked it up (I can't keep the order straight) they said it was >> acceptable either way. I don't recall who that was, but I don't think >> it was Wikipedia, rather someone a bit more authoritative. > > Rick, > > Oh sure. This is a long-standing joke between me and comp.dsp, although > I may be the only one who finds it funny...Ok, Henny Youngman you aren't... but if that's your joke, I'll go along... Rick
Reply by ●October 20, 20122012-10-20
Randy Yates wrote:> rickman <gnuarm@gmail.com> writes: > >> On 10/18/2012 8:04 AM, Randy Yates wrote: >>> Robert Adams<robert.adams@analog.com> writes: >>> >>>> In a sigma delta ADC, >>> >>> and by the way, it's "delta sigma"! >> >> >> As long as you want to nitpick, (or is it nitpik?) the last time I >> looked it up (I can't keep the order straight) they said it was >> acceptable either way. I don't recall who that was, but I don't think >> it was Wikipedia, rather someone a bit more authoritative. > > Rick, > > Oh sure. This is a long-standing joke between me and comp.dsp, although > I may be the only one who finds it funny... ><to the tune of "Boomer Sooner".....> http://www.youtube.com/watch?v=YpMdIHgDmCA Delta sigma! Delta sigma! Delta sigma! Delta sigma! Delta sigma! Delta sigma! Delta sigma! Delta sigma! (repeat ad idiotium) Now Randy is also a songwriter. -- Les Cargill
Reply by ●October 20, 20122012-10-20
glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:> Al Clark <aclark@danvillesignal.com> wrote: >> "Vladimir Vassilevsky" <nospam@nowhere.com> wrote in >> news:0YidnSblm_h87R3NnZ2dnUVZ5uydnZ2d@giganews.com:> (snip on using 256 ADCs to reduce noise)>>>> Assuming that all the various noise sources are orthogonal. >>>> Good luck with that. > >>> Analog sources of noise are uncorelated. External sources of noise could >>> be taken care off. Having true 24 bit performance is possible with >>> careful design.>> Some of the noises are uncorrelated such as the johnson noise of the >> resistors. You are likely to have noise from correlated sources as well.(snip, then I wrote)> But the ADC non-linearities won't cancel.> Now, say you (carefully!) dither the ADC input, and then either > subtract it later or arrange it so that the sum averages out.> Maybe you can get the effect of 256 ADCs using only one.I thought there might be more comments on this, but not so far. It seems interesting enough, though. If you can accurately enough dither the input to the ADC, then you can average out much of the non-linearity and get more bits, though at a lower rate. -- glen
Reply by ●October 20, 20122012-10-20
Check this out for the "anti delta-sigma" viewpoint. Apparently Nyquist didn't know what he was talking about. http://www.mother-of-tone.com/creation.htm
Reply by ●October 20, 20122012-10-20
On 10/20/2012 3:07 PM, Robert Adams wrote:> Check this out for the "anti delta-sigma" viewpoint. Apparently Nyquist didn't know what he was talking about. > > http://www.mother-of-tone.com/creation.htmYeah, he says the tone is 1 kHz and the ripple in the third waveform is from the filtered steps in the "common" process. I think he may be correct that the "ripples" are caused by filter responses to the transients. That is how a filter responds to an impulse, it displays the impulse response, right? But if you look closely at the second waveform image, from his ADC/DAC playback, you will see steps resulting from not having filters. What is not so clear is the result of the aliasing of frequencies above the Nyquist rate. I'm not sure what test would show this clearly, but this one isn't it. I guess just looking at a square wave might do it. The corners should be distorted. Why are there so many people who think they are smarter than people like Nyquist? In another group I have been having a discussion with a fellow who thinks he needs to use a GA144 multi-processor device to study OAM (orbital angular momentum in radio waves) because it will let him see quantum effects. "The thing that makes the GA144 special is that the electrical circuit between input pin and counter is the smallest it could be, so there could be very small quantum effects that would probably not occur with a conventional ADC setup." Where do all the kooks come from? Rick
Reply by ●October 20, 20122012-10-20
On Sat, 20 Oct 2012 12:07:39 -0700 (PDT), Robert Adams <robert.adams@analog.com> wrote:>Check this out for the "anti delta-sigma" viewpoint. Apparently Nyquist didn't know what he was talking about. > >http://www.mother-of-tone.com/creation.htmThat's awesome. I especially like the bit about mounting it on a spruce "musical sound board" for favorable microphonics. Way too much to comment on there, but thanks for the link! That was very entertaining. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
