Apple has blessed its latest iMacs with an improved 96kHz-supporting DAC (digital-to-analogue converter) and support for high-impedance headphones, according to a newly published Apple support document spotted by MacRumors.
The 3.5mm-jacked audio output stage on the refreshed 24-inch M3 iMac that has recently launched (and, it seems, on a handful of its recent Mac laptops too) has DC power load detection and adaptive voltage output features that can detect the impedance of connected wired headphones and better adapt its output for optimal sound quality.
More specifically, according to the document, ‘when you connect headphones with an impedance of less than 150 ohms, the headphone jack provides up to 1.25 volts RMS. For headphones with an impedance of 150 to 1k ohms, the headphone jack delivers 3 volts RMS. This may remove the need for an external headphone amplifier’.
Essentially, if a pair of headphones has a high impedance (measured in ohms), it will need more power to generate a sound that’s loud enough. So if a pair has a 32-ohm impedance, it can generally be more efficiently driven by a lower-level output signal from a phone or laptop etc, while a pair with a 600-ohm impedance will require more robust amplification capable of overcoming that high resistance. The former is more common nowadays, even in higher-end pairs (the Beyerdynamic T1 3rd Gen is one example), though Sennheiser and Beyerdynamic still have premium, high-impedance models in their catalogues.
Dealing with higher-impedance headphones is one thing a dedicated DAC/headphone amp generally offers over those integrated into everyday source devices such as computers, laptops and phones, another being sound quality improvement due to typically more sophisticated conversion architecture – clock circuits, power supplies, the chip itself etc.
With Apple making the effort to cater for high-impedance headphones in select iMac/Macs, it looks less likely that Apple will make an external DAC of its own to work with not only its computers/laptops but also with its iPhones and iPads. And considering the quality of Apple’s audio devices and the mark they’re certainly capable of making in the portable DAC space, this is a shame.
When Apple started offering hi-res streams on Apple Music, I thought it might produce a higher quality DAC than its fundamentally crude Lightning-to-3.5mm adapter (which is essentially a 24-bit/48kHz-supporting DAC and low-power amplifier that arguably acts as more of an 'enabler' than an 'improver'). But rumours of a switch from Lightning to USB-C in the iPhone were strong soon after that time, quashing thoughts of any new Lightning accessories, and then of course the iPhone 15 came and marked that transition earlier this year. As I penned following its arrival, would Apple now work on a slim USB-C DAC dongle (in the same vein as the Astell&Kern HC3) that supports hi-res up to 24-bit/192kHz and gives the iPhone 15 – and indeed its other devices – a big boost in sound quality? (An upgrade on its now USB-C-to-3.5mm 'enabler' dongle.) I would think that a relatively affordable, Apple-branded, USB-key-size device marketed at 'unleashing' the true potential of Apple's Hi-Res Lossless streams would make sense.
My hopes for an Apple DAC aren’t completely dashed, though if one was on Apple’s roadmap, the company probably wouldn’t have gone to any lengths to improve the iMac’s built-in DAC stage. Sigh.
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