[LAU] 24-bit files and hisss.... GOT IT

Arnold Krille arnold at arnoldarts.de
Tue Feb 17 02:13:02 EST 2009


On Monday 16 February 2009 22:14:41 Fons Adriaensen wrote:
> On Mon, Feb 16, 2009 at 09:27:18PM +0100, Arnold Krille wrote:
> > Are they really upsampling?
> > I was under the impression that they use one fast converter (far faster
> > then the sampling rate you hear) and the (de-)multiplex the signal to the
> > various channels. Should be easier than syncing several converter clocks.
> AFAIK nobody is doing that today. Some of the very early
> Sony converters for recording digital audio on video tape
> used to do this, compensating for the half sample delay
> on the second channel by the same trick on playback.
> Just consider this: a very good digital antialiasing
> filter operating at 8 * Fs (i.e. 8 * upsampling) costs
> almost nothing if integrated on the DA chip. An analog
> one for 44.1 or 48 kHz would require precision components,
> very careful board design, and probably manual alignment
> of each individual board. The choice is easy to make...

Thanks for that! I guess the one who told me my information (a phd here at 
university) had only knowledge from the earlier days of digital sound.

> > The devices I work with on the other hand go exactly
> > the other way, they  combine several 1GS/s adc's to
> > have one 4GS/s adc. But they face their own set of
> > clock-sync problems...
> I imagine they have !! The fastest one I was involved
> with was 1G, it drove most of the design team crazy,
> and required a collection of dirty tricks to get it
> interfaced to an FPGA, but that was five years ago...

I am glad I buy the finished product where the signal goes in and digital 
memory blocks come out via pci!

But not only do they sync up to four AD-converters to get one channel with 
4GS/s (current state of the art is 8GS/s!), they also sync several of these 
devices to act as one digital oscilloscope with multiple channels. They do the 
syncing by 10MHz clock and somehow manage to distribute the trigger event to 
all devices involved. Quite spooky and lot of hf to deal with.

Anyway, I wish I knew as much as you, Fons, about DSP. Current results (which 
I am presenting tomorrow) aren't really encouraging...

Have fun,

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