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Re: [newtech-1] Smartphone DAC clock frequency

From: Richard D.
Sent on: Wednesday, December 19, 2012 8:36 PM
Your maximum transmissible frequency will always be a function of your sampling rate.  The highest frequency you can encode digitally will be half your sampling rate (the Nyquist frequency).  If the hardware is sampling at 48kHz, then 24kHz is the best you can produce unless you circumvent the hardware and reprocess the digital signal at a different rate by getting the signal out digitally and then processing it in an external DAC capable of higher sampling rates (and thus higher Nyquist frequencies).  I've noticed this seems to be the preferred workaround for those who've discussed this issue online, but that requires you to market additional hardware to transmit the signal from the iOS device.  There are certain harmonics generated in the conversion process above the Nyquist frequency, but these are usually filtered out at the hardware level as unwanted conversion artifacts (i.e. noise).  Since the DAC is part of the integrated circuitry, I don't think it's possible to force the DAC to sample at a higher frequency or circumvent the filtering, especially not at the iOS media layer since this is done at a much more fundamental level. 

But I'm happy to be proven wrong.  It would be nice to control this functionality, but I'm imagine the sophistication necessary to provide this functionality to developers was cost prohibitive as far as Apple was concerned since it would require engineering a capability above and beyond what was required by most, if not virtually all potential applications.  It'd be like trying to get the performance of a Ferrari out of a Honda.  They just aren't engineered to the same standards.  

Richard

On Dec 19, 2012, at 7:44 PM, Kshitij wrote:

Hello Guys,

We are working on a project in which we want to increase the clock frequency of the speaker DAC to beyond 48 kHz. Eventually, we want to be able to transmit (ultra)sound frequencies more than 24kHz. First, is it even possible to control the DAC frequency or it is hardwired to a fixed value ? Second, in case the DAC clock frequency can be controlled, what is the maximum frequency to which it be set. Right now, we are looking at iphone 4S and Samsung S3.

A side note -- I am aware that at higher frequencies, the electronics and not the clock frequency may limit the maximum transmissible (ultra)sonic frequencies. But, for now we are focusing on looking at the effect of DAC clock frequency on maximum (ultra)sound frequency that can be transmitted.

Any inputs will be much appreciated,

Best,
Kshitij


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Kshitij Yadav, PhD.
Udacomm Inc.
New York, NY 10027
(e) [address removed]
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Udacomm.com
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