Audio Quality

The iPhone 6 is the first non-Android phone to be put onto the Audio Precision APx582 for audio testing. The exact same test tones are used as with Android devices, but they are played back through iTunes at maximum volume. We use the same four static loads as we did with the HTC M8 and Samsung Galaxy S5 for the results you see in the table below.

  15 Ohm 33 Ohm 150 Ohm 330 Ohm
Dynamic Range 84.155 dB 92.281 dB 92.223 dB 92.160 dB
THD+N 5.873% 0.0054% 0.0032% 0.0032%
Crosstalk (L) -49.608 dB -56.239 dB -71.721 dB -77.966 dB
Crosstalk (R) -49.831 dB -56.459 dB -72.191 dB -77.983 dB
Output Power 44.04 mW 26.39 mW 6.614 mW 3.072 mW
Output Voltage 812.7 mVrms 933 mVrms 997 mVrms 1,007 mVrms
Relative Level (20Hz - 20kHz) ±0.088 dB ±0.088 dB ±0.089 dB ±0.088 dB
The first thing to notice is the 15 Ohm load test. At maximum volume, with a -0dBFS signal the amplifier section in the iPhone 6 enters clipping. You can reduce the volume to avoid this, but it does not do as well with really hard loads as the M8 does. You can see the 1kHz sine wave for that below, with the amp clearly clipping at the bottom.
iPhone 6 997 Hz Sine Wave 0dBFS, 15 Ohm Load
For most testing I focus on the 33 Ohm load, as most in-ear headphones have a rated impedance around 32 Ohms. A data comparison to the HTC M8 and the Galaxy S5 is in the chart with the S5 as the clear loser.
  HTC M8 iPhone 6 Galaxy S5
Dynamic Range 92.074 dB 92.281 dB 91.921 dB
THD+N 0.0152% 0.0054% 0.0505%
Crosstalk (L) -64.780 dB -56.239 dB -44.767 dB
Crosstalk (R) -64.329 dB -56.459 dB -44.804 dB
Output Power 47.63 mW 26.39 mW 10.63 mW
Output Voltage 1.254 Vrms 933 mVrms 592.4 mVrms
Relative Level (20Hz - 20kHz) ±0.664 dB ±0.088 dB ±0.081 dB
Compared to the M8 the iPhone 6 isn’t quite as powerful, but it has lower THD+N and a much better relative level. The relative level isn’t a big deal, as a variation of 0.5dB is unlikely to be heard by most. That the THD+N is 1/3rd the value of that on the HTC M8 is more important, as the FFT below shows a very low noise floor on the iPhone 6 when compared to the one in for the M8.
iPhone 6 997Hz 0dBFS Sine Wave FFT
HTC M8 997Hz 0dBFS Sine Wave FFT
The crosstalk is also lower on the HTC, which is an area the iPhone 6 could certainly improve in. Digging into more depth on the THD+N results provides a bit more context. The HTC M8 has THD+N levels that start at 0.03% but after 2kHz it begins a steady rise up to 0.1% at 10kHz and past 0.2% at 20kHz. In contrast, the iPhone 6 THD+N is 0.03% until 500Hz, rises up to 0.06% at 5kHz, then back down to 0.03% at 9kHz, and peaks at 0.1% by 20kHz. The iPhone 6 will have slightly more midrange distortion but less treble distortion.
 
iPhone 6 THD+N Ratio Frequency Sweep
HTC M8 THD+N Ratio Frequency Sweep
If we leave noise out of it and look only at distortion then the iPhone 6 does even better. It has a distortion level of -95dB out to 10kHz and then it rises up to -82dB at 20kHz. The HTC M8 begins at -77dB for 20Hz, falls to -95dB until 2kHz, and then rises up to -56dB by 20kHz. The bass and midrange distortion is about equal, but the HTC M8 has far more distortion in the treble.
 
iPhone 6 Distortion (Noise) Frequency Sweep
HTC M8 Distortion (Noise) Frequency Sweep
Is one phone superior to the other? With the iPhone 6 and M8, I don’t believe so. The M8 is more powerful with lower crosstalk while the iPhone 6 has less distortion and better frequency response. Most notably the iPhone 6 has no results that indicate odd behavior, which we have seen with the Galaxy S5 and other phones. It is a well engineered headphone amplifier provided you do not need to listen to something at maximum volume with a 15 Ohm load.
 
Can Apple improve this? They could improve crosstalk, though some headphone companies like more crosstalk to help create an image more like a pair of stereo speakers than headphones. They could also support 24-bit audio which can improve on the SNR values here. The test tones are only 16-bit in nature, so the SNR maximum value is around -98dB. The HTC M8 may perform better given 24-bit test tones but would need a retest to verify this. Apple seems to have decided on using Lightning with an external DAC to push beyond 16-bit audio so we will have to wait for devices using that to see.
 
Audio hardware on phones can still improve a lot to get closer to where the best stand-alone products are. Those are capable of Signal-to-Noise ratios of -120dB or greater, and crosstalk of -110dB or more. How much those would be audible with headphones is uncertain, but when used as a source device with a stereo it may be audible. However, unless high-resolution audio downloads, like Pono or HD Tracks, really start to catch on I don’t see this being a main focus for most of the companies out there. The iPhone 6 is more likely what we will see going forward: good audio quality, but most importantly free of any major issues.
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  • bobobobo - Tuesday, September 30, 2014 - link

    solid phone, solid improvement. Reply
  • AppleCrappleHater2 - Tuesday, September 30, 2014 - link

    Worship the holy apple.

    The apple way, selling over expensive crap to stupid consumers that like to
    get robbed.

    This has been a disastrous launch in every respect. The iwatch is such an
    ugly piece of crap, it is truly unbelievable how a company, formerly known for
    its remarkable design, dares to put out such a crap ton of shit. Some
    characteristics are glaringly obvious and inherent to it: over expensive,
    hardly innovative, limited functionality and usability (need of an iPhone to
    make it work), looks exactly like a toy watch and so on.

    There are of course way better smart watches out there, especially from the
    likes of Samsung, Sony, Motorola, Asus, LG, simply put, there is no need for
    another piece of over expensive junk.

    The iPhone 6 is technologically stuck in pre-2011 times, a base model with
    a capacity of 16GB without the possibility to use SD cards isn't even funny
    anymore. The screen resolution is horrendous, it isn't water proof, shock and
    dust resistant, it offers nothing innovative, just some incremental
    updates over its predecessor, both lacking severely behind their competitors at
    their respective launch dates.

    Now the Iphone 6 Plus offers a „Retina HD“ screen, full 1920x1080p, oh wow,
    where have you been for the past 4 years apple, talk about trailing behind.
    That’s pathetic. The interesting thing about that is the fact that apple
    always manages to sell backwards oriented, outdated crap to its user base, all
    while pretending to be an innovative technology leader. The similarities
    regarding any form of sectarian cult are striking.

    You gotta love how Apple always comes up with new marketing bullshit terms,
    aka "Retina HD", with the intention to manipulate its users while preventing easy
    comparisons with its competitors by withholding the actual specs. Apparently it’s
    not enough to have a 1080p screen, you have to call it "Retina HD" to make those
    suckers buy it, otherwise someone could look at the 4K Amoled and Oled screens
    form LG and Samsung devices and get outright disappointed. Same goes for
    everything else. Every outdated „feature“ needs to get its own marketing label
    to persuade buyers with crappy „experience“ and „usability“ ads, while covering
    the truth with marketing gibberish, knowing full well that only a fraction of
    aforementioned buyers cares to look at the facts and dares to compare them.

    Car engines come to mind. For comparisons shake let’s look at a 1.0 liter, turbo
    charged petrol engine and a V8 compressor. What’s better should be obvious, but
    by calling the former an „ecobooster“, thus giving it a special marketing label,
    this joke becomes a „feature“, something positive that can be added tot the list
    of features of a car.

    By doing so a negative aspect is transformed into a positive one, the
    reality is distorted, non tech savvy buyers are manipulated and comparisons are
    made more difficult (another layer of marketing bullshit to overcome), well done
    marketing department. You see , if something is seriously lacking (of course for
    profit, what else), don’t bother explaining, just give it a nice marketing term, distort
    reality, make it a feature and call it a day. Fuck that!!

    FACT: Apple has been forced to copy Android in style and size for
    years because people abandoned their tired, moribund and fossilized
    devices for superior and innovative Android devices.

    Steve Jobs said no one should want a 7" tablet until everyone went and bought
    Android devices forcing Apple to copycat with the iPad Mini. Apple
    didn't think anyone wanted a phone screen larger than a business card
    until they all bought Androids thus forcing the arrival this week of the
    iPhone Galaxy and iPhone Galaxy Note clone phones.

    Swipe down notifications that don't interfere? Copied from Android and WebOS. Siri?
    Bought and ruined from a private developer; Google Now crushes it.
    3rd-party keyboards? Welcome to 2010, iChumps! Widgets? Welcome to 2009
    except you can't place them on your home screen. Live wallpapers and
    hidden icons? Maybe Apple will get around to copying those in iOS X in
    2016. Who knows.

    Apple lacks creativity and honest people acknowledge it. Steve Jobs gets credited as an
    innovator when all he was, was a huckster who'd spot someone else's tech, polish it up nicely,
    then slap a gnawed fruit logo on the back, charge a premium price and
    wait for the rubes like Jim Smith to hand over their cash like the good
    iSheep they are.

    But after that initial iteration, Apple is incapable of actually innovating something new.
    They literally cannot make a product until someone else shows them how and they copy it.
    They are also unable refine things because they believe to improve is to
    admit something was imperfect the first time. (This is why QuickTime 4
    had a legendarily terrible UI that was never changed through QT7 a
    decade later.) All they can do is make things incrementally thinner or
    faster but it's just minor refinements since they can't invest their way
    out of a wet paper bag.

    For all their squealing about Retina displays, they never even had a HD display until now;
    8th time is the charm, though you need the iPhone Galaxy Note to get the 1080p that many Android
    users have had for at least a year and is now considered
    bare-minimum spec. At the rate Apple drags along, QHD screens should
    arrive in 2018. Maybe. A graphic went around after the reveal comparing
    the iPhone Galaxy to the Nexus 4 from 2012. Exactly.

    The Apple Iphone 1 and Ipad 1 might have been innovative at their time,
    but since then, the bitten apple has been continuously rotting from the inside
    outwards, always swarmed by millions of Iworms which regale themselves with its
    rotten flesh, not forgetting all other Americans who support apple by means of
    their tax dollars to finance its bought US Treasury/Government bond interest rates.

    Last but not least, every Apple product includes a direct hotlink to the NSA,
    free of charge, something that might make it a good value, after all.

    Ceterum censeo Applem esse delendam.
    Reply
  • esterhasz - Tuesday, September 30, 2014 - link

    Since we're quoting Cato today, here's a good one: "grasp the subject, the words will follow". Reply
  • uhuznaa - Tuesday, September 30, 2014 - link

    You seem to be a tiny bit obsessed. Reply
  • iphone6splus - Tuesday, September 30, 2014 - link

    Yet, he didn't comment on Touch ID. Reply
  • kevin_newell - Thursday, October 09, 2014 - link

    Apple is lagging far behind it's competitors both in user satisfaction (source: http://www.consumertop.com/best-phone-guide/) and innovation. I mean, who was first with large screens and phone cameras that work well in low light? It sure wasn't Apple. Reply
  • Caliko - Tuesday, October 06, 2015 - link

    A large iPhone is NOT innovation.

    Sorry iPhoney fan.
    Reply
  • lowtolerance - Tuesday, September 30, 2014 - link

    I can recommend some good therapists. You need one. Reply
  • vickyksoni - Monday, March 20, 2017 - link

    you can also read more details about iphone 6 at https://smarttopten.com/ as they have lot more information Reply
  • melgross - Tuesday, September 30, 2014 - link

    You sir, are a complete idiot! Reply

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