iPhone 5S Audio Quality
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These are measurements of the 3.5mm analog audio output of the iPhone 5S playing signals in its Music app.
Few people realize that Apple iOS devices have some of the best audio digital-to-analog converters and low-impedance headphone amplifiers available at any price.
As you can see, frequency response is ruler-flat from at least 10 Hz to over 20,000 Hz.
Let's increase the vertical sensitivity by five times and see if we can see anything amiss:
Nope, still flat.
Let's increase the sensitivity again by five:
Wow, this is as flat as audio devices get. The iPhone still has flatter response than most audio analyzers!
0.002% THD and harmonic distortion components at 1 kHz at 0 dBFS into 200KΩ at maximum output level.
The harmonic distortion is mostly second-order, just like a tube amplifier. Bravo!
0.00043% THD and harmonic distortion components at 1 kHz at -20 dBFS into 200KΩ at maximum volume setting.
Wow, almost nothing in audio is this clean: 0.00043% THD is unheard of. This is at -20 dBFS where much of the music lies.
0.0125% THD and harmonic distortion components at 1 kHz at -40 dBFS into 200KΩ at maximum volume setting.
This is at a very low recorded level; a level so low that almost nothing is recorded this low except for some sections of classical music, and the THD is still well below any audible level with actual music.
The measurements above are into a 200kΩ load, meaning this is what you'll see using the iPhone 5S as a line-level source into your HiFi system.
Let's see what it does driving 300Ω typical for a very high quality home headphone:
0.002% THD and harmonic distortion components at 1 kHz at 0 dBFS into 300Ω at maximum output level.
The THD is just as low as into 200kΩ and harmonic distortion again is mostly second-order, just like a tube amplifier. Bravo!
I didn't make measurements here into 32Ω, but when I have, it's also extremely good.
The iPhone 5S has an output source impedance of an ohm or so, making it better than most exotic headphone amplifiers with higher output source impedances.
Higher output source impedances lead to frequency response imbalances caused by the varying real impedance of actual headphones with frequency, and also leads to low-frequency distortion when driving real headphones.
The ultra-low output source impedance of the iPhone 5S is so low as to stop any of these potential problems.
As expected, the analog audio output of the iPhone 5S is extraordinarily good. Apple has more smart people and more resources than any other audio company on the planet, so as we see when it comes to audio engineering, the iPhone easily outdoes many so-called "audiophile" products.
For enjoying music, you will probably get poorer performance if you waste your time and money with outboard DACs or headphone amplifiers; the iPhone already has the best there is.
Why do commercial audio magazines tout external DACs and amplifiers? Because that what their advertisers are trying to sell!
The only reason to get an outboard headphone amplifier for use with the iPhone 5S is if you have high-impedance (100Ω or greater) headphones which may require more voltage output than the 1V RMS from iOS devices. In this case, you still don't need a DAC; the analog output from the iPhone will probably be better than that from an outboard DAC.
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30 January 2017