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Does the DAC on the iPhone 4S output 24 bit audio or does it downsample to 16 bit?

post #1 of 9
1/7/13 at 2:58pm
Thread Starter 
I cannot find anything authoritative, but I've seen three conflicting answers to this question:
(1) The iPhone DAC can't decode anything higher than 48khz/16bit
(2) The iPhone DAC decodes 24 bit, up to 48khz/24 bit
(3) iPhone is compatible with 48/24, but downsamples everything to 48/16 before the DAC converts to analog.

I know (1) is not true, because I can upload and playback 48/24 ALAC files on my iphone with no trouble, so it must be (2) or (3). Anyone know the answer?
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post #2 of 9
1/8/13 at 6:36am
Quote:
Originally Posted by JD NC View Post

I cannot find anything authoritative, but I've seen three conflicting answers to this question:
(1) The iPhone DAC can't decode anything higher than 48khz/16bit
(2) The iPhone DAC decodes 24 bit, up to 48khz/24 bit
(3) iPhone is compatible with 48/24, but downsamples everything to 48/16 before the DAC converts to analog.

I know (1) is not true, because I can upload and playback 48/24 ALAC files on my iphone with no trouble, so it must be (2) or (3). Anyone know the answer?

Your question seems poorly stated because there are so many different models of iPhone and different models use different DACs.

From a SQ standpoint 44/16 done well can give you the best sonics that you'll likely ever hear, and is easily capable of fully exploiting the sonics of even the best real-world recordings.
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post #3 of 9
1/8/13 at 7:53am
Thread Starter 
Quote:
Originally Posted by arnyk View Post

Your question seems poorly stated because there are so many different models of iPhone and different models use different DACs.
From a SQ standpoint 44/16 done well can give you the best sonics that you'll likely ever hear, and is easily capable of fully exploiting the sonics of even the best real-world recordings.

My model is the 4S (per the title), and I also have an old iPhone 4, which I believe uses the same DAC chip. I think the iPhone 5 uses a different chip.

Based on some further digging, I think (3) is the right answer. There are some third party FLAC and other music players on the app store and they all say that the iPhone hardware is limited to 16 bit playback. The developers are probably in the best position to know, and would certainly highlight 24 bit playback if it were available.

I don't want to get into it on the whole 24 bit v. redbook debate, but I'll grant you that redbook is great 99% of the time. However, even though the differences are extremely subtle, I can hear the difference between a 24 and 16 bit version of the same track on capable equipment. The differences may be more or less audible depending on your ears, but it's there. (Whether it's worth the extra disk space for the tiny quality increase is another question, of course.)
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post #4 of 9
1/8/13 at 8:14am
Quote:
Originally Posted by JD NC View Post


I don't want to get into it on the whole 24 bit v. redbook debate,

But that doesn't stop you from jumping right into it!
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but I'll grant you that redbook is great 99% of the time.

that would be 100.00% for redbook done right.
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However, even though the differences are extremely subtle, I can hear the difference between a 24 and 16 bit version of the same track on capable equipment.

You'd be the first known person to do that in a decent listening test.
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The differences may be more or less audible depending on your ears, but it's there.

The differences you hear are no doubt due to the fact that you aren't doing really good listening tests.

Here are some articles about proper procedures for doing a good reliable listening test:

http://www.hydrogenaudio.org/forums/index.php?showtopic=16295

http://en.wikipedia.org/wiki/ABX_test

http://www.audiocheck.net/blindtests_index.php
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post #5 of 9
1/8/13 at 9:40am
Thread Starter 
Quote:
Originally Posted by arnyk View Post

But that doesn't stop you from jumping right into it!

Like I said, I'm not going to get into it with you about the merits of 24 bit. I wanted to know an answer to a question, go no relevant replies, so I did some more digging and posted the answer for anyone who's interested. Hijacking the thread with your own opinions on the merits of the underlying question is not productive.
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post #6 of 9
1/8/13 at 10:29am
Quote:
Originally Posted by JD NC View Post

Quote:
Originally Posted by arnyk View Post

But that doesn't stop you from jumping right into it!

Like I said, I'm not going to get into it with you about the merits of 24 bit.

And yet again you choose to go on and on about exactly that!
Quote:
I wanted to know an answer to a question, go no relevant replies, so I did some more digging and posted the answer for anyone who's interested. Hijacking the thread with your own opinions on the merits of the underlying question is not productive.

As opposed to wasting time on sonically nonproductive technical exercises?

Given the mass of info that is already on the web talking about exactly the exact question you raised...

And of course given that there are in fact still no commercial DACs with true and genuine 24 bit performance, and certainly none with power usage profiles that are appropriate for a portable phone...
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post #7 of 9
1/14/13 at 2:06am
Quote:
Originally Posted by JD NC View Post

I cannot find anything authoritative, but I've seen three conflicting answers to this question:
(1) The iPhone DAC can't decode anything higher than 48khz/16bit

DACs don't decode anything, they convert digital signals to analog. The decoding happens in software, on the ARM cores in the iPhone.
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(2) The iPhone DAC decodes 24 bit, up to 48khz/24 bit

See 1). What codecs are supported is a matter of the playback software you are using, the DAC is irrelevant.
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(3) iPhone is compatible with 48/24, but downsamples everything to 48/16 before the DAC converts to analog.

Apple uses Cirrus Logic CODECs in their devices but they are custom parts so unless you get an Apple engineer on the line, you won't get a real answer. That said all non-custom CODECs cirrus sells now are 24bit/96khz parts, including their mobile parts. That doesn't mean that the iphone isn't limiting this to something lower though.

That said, even disregarding the lack of audible differences between 16 vs 24 bit audio given perfect hardware, I doubt you could even measure a difference given the noise floor in such circumstances. The amount of space for filtering and reconstruction within a cellphone is zero and the noise floor is high. As an example, here is Cirrus's mobile device stereo codec you'll see the dynamic range rating for that part is only 2dB higher for 18-24bit than it is for 16bit, and that is on a perfect testbed for the chip, not when its been stuffed onto a cramped PCB with tons of digital and RF electronics inside a metal case.
Edited by xianthax - 1/14/13 at 11:47am
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post #8 of 9
1/14/13 at 6:23am
Thread Starter 
Quote:
Originally Posted by xianthax View Post

DACs don't decode anything, they convert digital signals to analog. The decoding happens in software, on the ARM cores in the iPhone.
See 1). What codecs are supported is a matter of the playback software you are using, the DAC is irrelevant.
Apple uses Cirrus Logic CODECs in their devices but they are custom parts so unless you get an Apple engineer on the line, you won't get a real answer. That said all non-custom CODECs cirrus sells now are 24bit/96khz parts, including their mobile parts. That doesn't mean that the iphone isn't limiting this to something lower though.

That said, even disregarding the lack of audible differences between 16 vs 24 bit audio given perfect hardware, I doubt you could even measure a difference given the noise floor in such circumstances. The amount of space for filtering and reconstruction without a cellphone is zero and the noise floor is high. As an example, here is Cirrus's mobile device stereo codec you'll see the dynamic range rating for that part is only 2dB higher for 18-24bit than it is for 16bit, and that is on a perfect testbed for the chip, not when its been stuffed onto a cramped PCB with tons of digital and RF electronics inside a metal case.

Thanks for the help - yes, convert is the right word.

The main reason for my original question is that I have a small, but growing collection of 24 bit files in my itunes library, but I have separate 48/16 versions that I load onto my phone to conserve space, since I can't hear the difference with my current headphones. Disappointing that even if the hardware is capable of outputting of outputting the full 24 bit audio, the noise will overpower any improvement, but at least I'll save a few bucks on gear and storage space.
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post #9 of 9
1/14/13 at 11:31am
Quote:
Originally Posted by JD NC View Post

Thanks for the help - yes, convert is the right word.

The main reason for my original question is that I have a small, but growing collection of 24 bit files in my itunes library, but I have separate 48/16 versions that I load onto my phone to conserve space, since I can't hear the difference with my current headphones. Disappointing that even if the hardware is capable of outputting of outputting the full 24 bit audio, the noise will overpower any improvement, but at least I'll save a few bucks on gear and storage space.

If I were to venture a guess, they probably run it at 16/44.1, maybe 48, for two reason:

1) My guess is that the major 'custom' part of Apple's design is putting the noise canceling algorithms for the microphone in the codec hardware so they don't have to keep a high priority thread around on the CPU to do it. Lower bit rate reduces the processing needs which in turn reduces the power needs.

2) Power - Most modern DACs/ADCs use sigma-delta modulation. The difference between 16bit and 24bit isn't 'more bits' in hardware, its a higher clock rate (and in a CODEC, a slightly tweaked digital input, e.g. changes to the size of the shift registers, DSP register size, etc). Higher clock rate = more power. Apple is pretty obsessive about managing power usage so I doubt they would overlook this given the lack of tangible improvement.
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