RE: [newtech-1] Smartphone DAC clock frequency

From: Calvin C.
Sent on: Wednesday, December 19, 2012 9:11 PM

Apple licenses audio IP blocks from Cirrus Logic.  Specifically for the iPhone 5, there are two separate audio chips, one for the codec and the other for the class-d amp.  Chipworks dissected the phone and found the Apple chip (338S1117 Audio Codec) has master clock native support for 6, 12, 24, 13, 26, 19.2 and 38.4.  Cirrus has a configuration that looks exactly like this and unless it’s a private IP block for Apple, the limit is 48Khz.  So check out these specs:


I’m not saying this is in the iPhone 5 but it quacks and quacks. 

Also, from the software perspective, the API that can be set to arbitrary rates but what it really does in the intervening layer is choose the closest match and translate.  But anything that doesn’t match a hardware rate will slog the CPU, and anything above 48 is bumping up against a hardware limit.


TL;DR Kshitij you’re stuck at 48. 



Calvin Chu

Senior Technology Licensing Officer, Columbia Technology Ventures

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From: [address removed] [mailto:[address removed]] On Behalf Of Kshitij
Sent: Wednesday, December 19,[masked]:45 PM
To: [address removed]
Subject: [newtech-1] Smartphone DAC clock frequency


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,






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

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