iPhone 5 Audio Quality
Apple iPhone 5 (4.015 oz./113.8g). My biggest source of support is when you use any of these links, especially this link directly to them at eBay (see How to Win at eBay), when you get anything, regardless of the country in which you live. Thanks! Ken.
I'm discussing the iPhone 5's sound quality for playing music via the iPhone 5's Music app as heard at its 3.5mm jack, either with headphones or plugged into a hi-fi.
I'm not discussing the built-in speaker or the telephone's performance.
If you ask, the built-in speaker is even better than earlier models, but I've never tried the phone (I use the iPhone mostly as a camera and as a music player, but not as a phone).
Perceived Sound Quality
Plugged into professional monitoring equipment as a sound source, the iPhone sounds great. Be sure to make good music transfers, disable the cell phone (preferences > airplane mode, and then turn wi-fi back on if you need it) so it doesn't send RFI into your system which will sound like buzzing on GSM/AT&T, and leave the iPhone's level set to maximum, and just plug it into your hi-fi. Wasting time with "Audiophile" DACs and other fluff usually degrades the sound more than just using the self-powered iPhone 5 directly as a source.
Used directly with headphones plugged into the 3.5mm jack (use the Grado adapter for real headphones with 1/4" plugs), it also sounds swell so long as its usual 1V RMS maximum output is enough. It even sounds swell with the Audeze LCD-3, with which it goes plenty loud. It's plenty for 32 Ω headphones, but for classical music with 600 Ω headphones, might not be. No problem, just add a great headphone amplifier like the Woo Audio WA7 if you need more headphone output.
There isn't much difference between different iPods, iPhones and iPads; all pretty much have ultraflat response, near-zero output impedances and deliver 1 V RMS full-scale. People who hear huge differences in bass or treble aren't comparing them competently, or are comparing the internal speakers or something else.
I have not performed my Acid Test where I A/B the iPhone 5's output playing a CD recorded via iTunes as an ordinary AAC file versus a real, dedicated CD player playing the same physical CD, but when I did spend several hours A/Bing an iPod Touch 4G with 160 kbps AAC VBR files against the original CDs, I wasn't able to hear any difference at all as monitored with a STAX SRM-T1 amplifier and STAX SR-007 MK II electrostatic headphones. (MP3 files sound much worse at the same data rates, I'm not talking about them.)
This setup lets me hear everything, like the shape of the room in which the recording was made, and I couldn't hear anything different after several hours of careful listening, much less better or worse, between a 25-pound dedicated CD player and the same CD played out of my iPod Touch 4G as coded and compressed via iTunes – and I can hear a quarter decibel level shift, I can hear 0.1 % THD, and I can hear -2dB drop at 20 cps. Unlike old audio reviewers, my hearing still tests perfectly. I can hear every page turn, every seat creaking, I hear the conductor humming, the soloists breathing and I hear fingers hitting the keys or frets, but all I heard when A/Bing was exactly the same thing out of each when I flipped my A/B switch. Even the shape of the room was unchanged, something you can't even hear in most conventional hi-fi systems.
Of course it is very difficult to setup such a test with the levels and timing matched, but when you do, the whole iPod audio ecosystem is transparent. If you're hearing differences, you just don't have everything matched; most CD players need a 6 dB pad to match the iPhone's output and you have to get both players in perfect sync and have an instantaneous A/B switch, otherwise your test will be showing the limits of your test system and not differences between your CD player and the iDevice.
I suspect the iPhone 5 will also pass the Acid Test; in any case, it sounds great subjectively as a source.
Audio Quality Measurements
I used a $50,000 Rohde & Schwarz UPL audio analyzer to perform these measurements.
The traces are color coded for the Left Channel and for the Right Channel. When they don't lie on top of each other, it's due to channel imbalance.
I loaded the CBS CD-1 standard test CD into iTunes as ALC files, synced my iPhone 5 via iTunes 10, and then played-out from the iPhone 5's standard Music app at maximum gain (volume) under battery power.
Output Source Impedance
Output Noise Levels
-106.8 dBV, A-weighted, playing zeroes (silence).
-116 dBV, A-weighted, idle.
iPhone 5 Frequency Response, 200 kΩ load, 1 V RMS output.
As expected, the iPhone 5's response is ruler-flat.
Let's expand the scale and look more closely:
iPhone 5 Frequency Response, 200 kΩ load, 1 V RMS output, expanded scale.
Not bad; down only 0.01 dB at 20 Hz and -0.08 dB at 20 kHz, flatter than most labs can measure.
Let's plug in a headphone and see what happens:
iPhone 5 Frequency Response, driving Ultrasone Edition 8 (32Ω).
The near-zero (4.5 Ω) output impedance of the iPhone 5 is much better (lower) than most dedicated headphone amplifiers, even most exotic audiophile amps, and therefore its response is not significantly affected by the headphones in use. Most dedicated amplifiers have about ten times the output impedance of the iPhone 5, and allow about a dB or two of false bass boost with the Ultrasone Edition 8. With the iPhone 5, the sound is accurate and well controlled.
Total Harmonic Distortion
This is true THD only, which includes harmonic components only and ignores non-harmonic content (noise):
iPhone 5 THD, 1 kHz, 200 kΩ load, 1 V RMS.
iPhone 5 Harmonic Distortion Spectral Content, 1 kHz, 200 kΩ load, 1 V RMS.
To my surprise, the harmonic content is mostly second-order, with higher harmonics at least about 15 dB down from the second harmonic. I'm more used to seeing this sort of signature from tube amplifiers!
The distortion lowers if you lower the volume setting:
iPhone 5 THD, 200 kΩ load, 100 mV RMS output at 0 DBFS (gain at -20 dB or about one-half volume).
OK, enough of driving resistors, which represents what happens when you plug the iPhone 5 into hi-fi gear.
Let's start plugging in real headphones and see how it performs driving real loads, which are measurements you'll almost never see elsewhere:
iPhone 5 THD driving Beyer DT880 (600 Ω), 1V RMS.
No problem here; driving a real 600 Ω headphone is just as clean as driving another amplifier.
Let's see what happens if we drive a 37.5Ω resistor:
iPhone 5 THD, 37.5 Ω load, 1 V RMS.
Again no problems. There's a tiny bit more distortion as expected, but nothing significant.
Let's now make it tough, and try driving some real 32 Ω headphones:
iPhone 5 THD driving Ultrasone Edition 8 (32Ω), 1 V RMS.
AHA! Now we have distortion while driving a real, tough load. But wait: this is at full volume, and at this level, the headphones were generating far more distortion out of their own distress (not shown here) than any distortion of the electrical signal.
Compared to most dedicated audiophile amplifiers, the iPhone 5 still drives the Ultrasone Edition 8 with less distortion — and this is at a deafening 1V RMS (113 dB SPL) to which I haven't pushed other amplifiers driving 32 Ω headphones.
Let's look at the harmonic content when pushed this hard at 61 Hz:
iPhone 5 THD driving Ultrasone Edition 8 (32Ω), full output at 0 DBFS at 61 Hz.
Mostly third harmonic at about 0.03% (-70 dB), but the headphones themselves were hideously distorting far more than that at 61 Hz from their own mechanical limitations (not shown).
Conclusion: the iPhone 5's own distortion is insignificant compared to the distortion of the headphones themselves at this level in the bass.
Let's bring it down from deafening (113 dB) to merely too damn loud (93 dB SPL), with a 100 mV signal. In other words, I turned the iPhone 5's volume down from FULL to about halfway:
iPhone 5 THD driving Ultrasone Edition 8 (32Ω), 100 mV RMS output at 0 DBFS (gain at about -20 dB or about one-half volume).
AHA! As expected, much less distortion, and far less than most exotic dedicated headphone amplifiers at low frequencies (see my other audio reviews) when driving real 32Ω headphones.
Peak Overload Capacity
Real music never has this problem, however we can generate pathological test signals which can overload less able audio equipment whose designers misunderstand how analog signals map when sampled, quantized, and then played back. In other words, transient signals can and should exceed the 100% level of a sine wave at full scale.
This still has never mattered with real music, but with some of the overlimited, over compressed and composite-clipped crap getting mastered onto CDs by deaf producers who think music buyers prefer the loudest, as opposed to the best, music, many popular CDs today (and therefore also the LPs, CDs and SACDs mastered from the same files) are already recorded with distortion and overloads never considered when the CD and digital audio was first designed back in the 1970s, which can stress weaker playback chains.
Let's see how the iPhone 5 handles this overload, specifically with a pathological 100% square wave signal that excites full ringing. Ideally the output should be a square wave with only odd-ordered harmonics, and no even-ordered harmonics. Let's see:
iPhone 5 Harmonic Distortion Spectral Content, 1,002.27 Hz Square Wave, 200 kΩ load, CD-1 track 16.
Bravo! Even-order harmonics are way down; no need to worry about playing crappy music at full level when using the iPhone 5 as a music source for your hi-fi.
Below is a devious test I devised that shows actual digital jitter as detected in the analog output. This is a very narrowband FFT of a 10,007 Hz sine wave.
Ideally it's just one spike, and any jitter is seen as a risen skirt or spikes around it:
Narrowband FFT of 10,007 Hz sine wave at full scale, 200 kΩ load, CD-1 track 9.
This is pretty good, as expected. Unlike external DACs which all pick up jitter as noise enters interconnects and confuses the clock recovery circuitry, CD players and iPods all use their own internal original clock signals to drive their DACs. In other words, one-box players never need to recover a clock because they still have it, while TOSLINK and SPDIF and USB all have to try to recreate the lost clock signal because those interfaces lack a dedicated, parallel clock signal connection.
In any case, the overall skirt is quite low, as good as a real CD player and better than many external DACs, but the individual spikes are a little higher.
I wouldn't worry about any of this; all these spikes are completely inaudible in the presence of the 10 kHz sine wave of which they are part (as the 10 kHz sine wave jitters it changes frequency), with the 10 kHz sine wave still 100 dB louder than any of the nearly identical (in frequency) spikes.
Confirming what I hear with critical listening, the iPhone 5 is a wonderful high-fidelity audio source. While publications funded mostly by advertisements from makers of expensive cables, power conditioners and outboard DACs don't want you to know this, the iPhone 5 is a better audio source than most DACs will be when connected to a computer or CD transport. The only difference is that the iPhone has a level 6 dB lower than a proper CD player, but the iPhone still has more output at 1 V full-scale than some outboard audiophile DACs! (Stereophile wrote that "The iPod's measured behavior is better than many CD players" back when the iPod first came out and was only considered as a toy and not as a better player than most of the exotic fluff gear out today.)
The iPhone lacks a fan or hard drive, so it runs silently as it plays from its buffered solid-state memory.
The iPhone 5 has the additional benefits of being self-powered, so you have no ground loops as you will when using AC-powered gear or anything connected to a computer via a electrically conductive cable.
Ignore those who confuse the iPhone with crappy MP3 players; the iPhone has wonderful audio quality for serious music listening either directly with good or great headphones or plugged into the rest of your high fidelity system.
Enjoy your iPhone!
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