[sdiy] Can't find 1-bit ADCs

cheater cheater cheater00social at gmail.com
Sat Jun 11 01:05:28 CEST 2022


Wow, that's a lot! I had no idea!

Can't one use something like a 16-bit 500 kHz ADC/DAC, and a slow
cutoff at 22 kHz? Wouldn't the "just out of band" stuff be above 500
kHz anyways?

On Sat, Jun 11, 2022 at 12:28 AM Mike Bryant <mbryant at futurehorizons.com> wrote:
>
> Well I googled " bergkristall cable elevator pyramids" and didn't find anything :-)
>
> The digitised audio signal contains the original signal plus various noise and distortion products, which hopefully if the correct jitter has been applied at the ADC are out of band.  But some will be only just out of band, and hence even if you are sampling at 96/192/384 kHz, you still need a fast cutoff filter.  This inherently has more group delay (not sample delay which can actually be as low as a single sample) than one with a slower cutoff.   The best ADC-DAC systems used to achieve about 2 to 3mS, but in recent years this seems to be down to as low as 800uS.  However I am not convinced they sound quite as good in live audio systems, but that's a subjective opinion of course.
>
>
> -----Original Message-----
> From: cheater cheater [mailto:cheater00social at gmail.com]
> Sent: 10 June 2022 23:12
> To: Mike Bryant
> Cc: Eric Brombaugh; synth-diy at synth-diy.org
> Subject: Re: [sdiy] Can't find 1-bit ADCs
>
> So are you saying my bergkristall cable elevator pyramids are a fad?
>
> I understand the point of removing the out of band distortion at the DAC, but if I use, say, a 13.1 MHz signal to transfer an effective "16 bit depth" 50 kHz audio signal over that, why does the in-band get delayed when the out-of-band gets low pass filtered away?
>
> On Fri, Jun 10, 2022 at 11:02 PM Mike Bryant <mbryant at futurehorizons.com> wrote:
> >
> > You can use DSD at any frequency if it's a self contained system.  Bare in mind that you will still need to move the quantisation noise and distortion products out of band at the D-A conversion at which you will have to introduce some delay.
> >
> > Also you need error correction on the transmission medium because DSD does propagate errors, whereas with PCM they just affect one sample.  Of course if it's the MSB of a PCM sample that error will sound like a click, but with DSD the error effect fades away over a much longer time.   But with a perfect transmission medium, there is in truth no real performance difference between the methods for the same bit rate, despite all the numerous webpages written on the subject.
> >
> >
> > -----Original Message-----
> > From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
> > cheater cheater via Synth-diy
> > Sent: 10 June 2022 20:12
> > To: Eric Brombaugh
> > Cc: synth-diy
> > Subject: Re: [sdiy] Can't find 1-bit ADCs
> >
> > Thanks, Eric. I thought 1-bit streams were a generic output and DSD was a very specific format - or is DSD used for such signals at any frequency?
> >
> > Do you agree with Tom regarding the latency?
> >
> >
> > On Fri, Jun 10, 2022 at 4:36 PM Eric Brombaugh via Synth-diy <synth-diy at synth-diy.org> wrote:
> > >
> > > The search term you're looking for is DSD - direct stream digital.
> > > There are ADC and DAC chips available for this format:
> > >
> > > https://www.ti.com/product/PCM4222
> > >
> > > https://www.analog.com/media/en/technical-documentation/data-sheets/
> > > AD
> > > 1955.pdf
> > >
> > > Eric
> > >
> > > On 6/10/22 06:40, cheater cheater via Synth-diy wrote:
> > > > Tom,
> > > > that's kinda what I want, but different.
> > > > I'm looking for a high audio quality and good DC precision (12
> > > > bits usable or better) ADC that will output 1-bit bitstream
> > > > output. I would prefer it to "full width" output (eg 16 or 24
> > > > bits) because I would prefer sub-1-sample delay - I'm basically
> > > > making a "digital audio snake" where the output of the ADC goes pretty much directly to a DAC.
> > > > If the chip does 4, 8, or 16 channels, that's even better (because
> > > > it's hopefully cheaper and smaller and lower power).
> > > >
> > > > A comparator isn't great, you'd have to run your own sawtooth
> > > > oscillator, etc, kind of annoying, and definitely not good for
> > > > audio quality. Won't /somebody/ please think of the golden ears...
> > > > But no, seriously, looking for good audio quality.
> > > >
> > > > On Fri, Jun 10, 2022 at 3:04 PM Tom Wiltshire <tom at electricdruid.net> wrote:
> > > >>
> > > >> It also depends a bit what you're going to do with the output. If you *actually want* a simple bitstream of the data, then the comparator is probably the way to go. There are some very retro eurorack delays done like this: 1-bit ADC, fed to pile of old RAM chips, out to an integrator. Example:
> > > >>
> > > >> https://modwiggler.com/forum/viewtopic.php?p=2631837
> > > >>
> > > >> Otherwise, if you want some more modern data format at the output (I2S or SPI or whatever) then who really cares how that is achieved? That'd be up to the ADC designers, and I'm happy to let them be the experts in that field!
> > > >>
> > > >>> On 10 Jun 2022, at 13:48, Steve via Synth-diy <synth-diy at synth-diy.org> wrote:
> > > >>>
> > > >>>
> > > >>> they were being a bit mean to you ;)
> > > >>>
> > > >>> I suppose no one advertises delta-sigma ADCs (which is I guess
> > > >>> what's talked about?) as having "1 bit", but by the number of
> > > >>> bits their data register has, and that won't be 1, as the things
> > > >>> are supposed to take the burden off of you, to make something
> > > >>> useful out of a signal sampled that way. You typically wouldn't
> > > >>> want to implement that in software, I'm pretty sure. (from my
> > > >>> superficial understanding of the topic. I've only ever used
> > > >>> those things as black box)
> > > >>>
> > > >>> cheater cheater via Synth-diy:
> > > >>>> I'm talking about actual ADCs meant for audio :)
> > > >>>>
> > > >>>> On Fri, Jun 10, 2022 at 12:17 PM Mike Bryant <mbryant at futurehorizons.com> wrote:
> > > >>>>> Far better to use the LM361.  Runs orders of magnitude faster and both edges have same speed so much more accuracy driving the feedback loop.
> > > >>>>>
> > > >>>>>
> > > >>>>> -----Original Message-----
> > > >>>>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On
> > > >>>>> Behalf Of Neil Johnson via Synth-diy
> > > >>>>> Sent: 10 June 2022 09:56
> > > >>>>> To: cheater cheater
> > > >>>>> Cc: synth-diy
> > > >>>>> Subject: Re: [sdiy] Can't find 1-bit ADCs
> > > >>>>>
> > > >>>>> cheater cheater wrote:
> > > >>>>>> I'm having a bit of trouble finding 1-bit ADCs. The kind that
> > > >>>>>> runs at something like 1.5 MHz-ish or higher to sample audio.
> > > >>>>>> Mouser only starts listing ADCs at 4.5 bit depth and google
> > > >>>>>> isn't helpful. How do I find them? Can someone suggest any devices?
> > > >>>>> LM311.  Classic 1-bit ADC.  Works up to ~3 MHz.
> > > >>>>>
> > > >>>>> Neil
> > > >>>>> _______________________________________________
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