Apple Lightning interface and Hi-Res
Following a letter from one of our readers quoted below, we have decided to shed some light on the decoding abilities of audio peripherals that you can directly interface with the Apple Lightning socket.
I am already a Sublime subscriber, and I’m thinking about upgrading to the Sublime + subscription, could you tell me if connecting Apple products (iPhone, iPad,…) that aren’t Hi-Res compatible to “Audeze” headphones (SINE, ISINE10 or 20...) equipped with a DAC (24 bits) on their cables could allow them to get Hi-Res quality?
Thank you for your answer.
The various audio devices (headphones and DACs, mainly) compatible through USB with Apple smartphones and tablets must conform to technical specifications issued by Apple and receive the company’s approval in order to get the MFI license (Made for iPod, iPhone, iPad), thus ensuring complete compatibility for the user.
Before talking about Hi-Res, let’s note that we at Qobuz have on occasion seen some devices equipped with a MFI-approved USB interface chip which, used alone, wouldn’t allow for the decoding of digital audio files above 16 bits at a 48 kHz sampling rate.
Why? Because of the inclusion in the USB chip of a DAC limited to this sampling, a condition that was probably part of the technical specifications in order to conform to Apple systems’ playback capabilities (16-Bit/48 kHz).
But, as we noticed during the test of the Denon DA-10 portable DAC, you can easily get around this restriction by using the I2S bus delivered by the USB chip in question and by decoding it with a conversion chip compatible up to 24-Bit/192 kHz.
Here’s what we wrote in the testing ground of the Denon DA-10 DAC:
Since the DA-10 possesses a specific input for an iPhone or an iPad, it uses a specialized integrated circuit that is certified “Made for iPod, iPhone, iPad” built by the manufacturer Rohm. It’s the BU94502MUV model compatible up to 16-Bit/48 kHz (on p. 33/72 of the datasheet), so with these devices’ playback capabilities, a precision that is absent, would it seem, from the DA-10’s datasheet, except on the Denon Japan website which indicates 24 bits (!) at 48 kHz.
It shouldn’t be possible to use the Qobuz Hi-Res application for i-Device from this input, as Rohm indicates (still on p. 33/72 of the datasheet):
12.2.4 WAV file format
This format supports RIFF WAVE.
22.05 kHz, 44.1 kHz, 12 kHz, 24 kHz and 48 kHz.
If you try to play a file created in any format other than above, the LSI immediately terminates decoding it.
But then, how can we explain that our decoding tests with the Qobuz Hi-Res applications have been successful up to 24-Bit/192 kHz?
According to us, this is most probably due to the fact that the DAC included in this chip, which is limited to 16-Bit/48 kHz, isn’t used by Denon, which only receives the I2S bus extracted from the USB signals and that this I2S bus, not restricted to 16-Bit/48 kHz, is processed and decoded by the other circuits of the electronics of the DA-10.
Still, this Qobuz for iOS application has since its launch overcome this sampling restriction by making the Hi-Res digital audio streams up to 24-Bit/192 kHz available on the Lightning socket of the Apple devices, which allowed for their decoding by every DAC able to establish a connection with an iPhone or an iPad, directly like the Denon DA-10, or through the Apple Camera Kit for most other DACs.
As it also happens, things seem to have changed at Apple on this sampling matter since the release of the iPhone 7, which wasn’t equipped with a headphone output and was sold with a Lightning to stereo 3.5 mm Jack adapter, actually a tiny DAC with headphone amplifier that the manufacturer also sold as an accessory and to which we devoted this article, which allowed us to notice with our ears that Hi-Res was indeed processed by this model called Lightning to Headphone Jack Adapter.
Cirrus Logic, the famous digital-to-analog conversion chips manufacturer which had developed this adapter for Apple, also made available to other manufacturers a kit allowing them to create their own device in compliance with Apple demands in order to be MFI-certified.
Since, the devices—especially headphones that you directly plug in the Lightning socket—have multiplied, from many brands like Audeze, cited by our reader, or Philips, Sony, Pioneer, JBL...
All those headphones are thus able to provide a Hi-Res listening experience with Qobuz from an iPhone or an iPad if you have a Sublime + subscription, or with a Sublime subscription for the Hi-Res albums that you purchased.
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