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.
Video Quality Software
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  • thrasher32 - Tuesday, October 14, 2014 - link

    That must be some really good crack there chief Reply
  • GerryS - Wednesday, October 1, 2014 - link

    Absolutely. If it can't be built into the price of the product, there's no incentive to innovate, at all. Reply
  • perpetualdark - Friday, October 3, 2014 - link

    Not true, you innovate to stay in the game, not to increase your price point. Part of the "innovation" of the android flagships has been their ability to increase technology, form, and function while reducing or maintaining costs. Both the M8 and the S5 were selling for $99 on contract within a month of launch (by Verizon). Apple might have sold a lot of phones in this launch, but that was mostly due to the fact that there hasn't been an "innovation" in several years, and very little reason to buy an Apple product for at least 2 generations. Just keep watching to see how sales hold up after the initial storm is passed. In a few months when you can buy an S5 or M8 for $99 on contract, or an iPhone for $299, which do you think will sell better? And in 6 months, both companies will have the next gen of flagship out, with superior specs across the board and will launch at the same price as Apple, because the iphone 6 will STILL be $299. Reply
  • bigstrudel - Tuesday, September 30, 2014 - link

    Samsung uses Off-the-shelf SoC's for every flagship device outside of Korea. Nothing impressive about that. Reply
  • techconc - Thursday, October 2, 2014 - link

    @danbob999 - Samsung's SoC designs are basically equivalent to Apple's early A4 and A5 work. They essentially just use off the shelf reference designs and put them together to meet their own specifications. Yes, there is some work involved with doing that, but to date, this hasn't been a competitive advantage for Samsung like it has for Apple. In fact, Samsung ends up using Qualcomm chips for a very large percentage for their devices. Likewise, putting them in the same league as what Apple, Qualcomm or even nVidia is doing isn't quite right. They're not in the same league design wise.
    Samsung attempts to add layers of customization (Touchwiz, etc.) on top of Android, but it just feels like a clumsy layer on top and ends up dropping performance and resources for the device overall. Such customizations are no substitute for writing your own OS and controlling the entire technology stack. That's why a Samsung phone will always feel clumsy as compared to an iPhone. Samsung would have to to the Tizen route to attempt to compete on that level.
    Reply
  • Chaser - Wednesday, October 1, 2014 - link

    Now this is amusing. The OS hasn't changed since it launch except for, wait for it: pull down notifications! Amazing. But seriously its the same floating blobs that sit in rows on a screen. Designed for teenagers and grandparents in mind. Reply
  • techconc - Thursday, October 2, 2014 - link

    @Chaser - Thanks for sharing your ...wait for it... ignorance on OS design and what's actually changed over the years. It should suffice to say that you clearly don't know what you're talking about. Reply
  • shm224 - Thursday, October 2, 2014 - link

    @techconc : Sure, would you mind giving us some examples of such "changes" in iOS? Reply
  • techconc - Monday, October 6, 2014 - link

    @shm224 - LOL! Not interested in doing a commercial for Apple and the listing surely wouldn't fit in a forum post. Google is your friend... If you're really interested, you can start with something like the Wikipedia entry for iOS and of course consult the release notes for each iOS release on Apple's developer site. Reply
  • michael2k - Thursday, October 2, 2014 - link

    What? It gained an app store, popup notifications, printing, multitasking, search, pull down notifications, pull up settings, folders, multiple homescreens, enhanced notifications (reply, dismiss, widgets), and file sharing. Reply

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