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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  • michael2k - Thursday, October 02, 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
  • akdj - Friday, October 03, 2014 - link

    Who uses their smartphone to sit and look at the UI? Or. Thats right. You. Can't find any apps that'll work? I'm on my springboard for a second or three. Like you said, pull down, enter the first letter or two of the software/app I'm going to use and click, it's open!
    No more just looking at the 'floating (?) blobs that sit in rows (like Android)non a screen. Designed for teenagers, grandmas, commercial and military pilots. Military operations you're clueless about and 95% of the Fortune 500 companies have deployed iOS.
    And unfortunately for you, if you're NOT an iOS user, I completely 'get it'. I've got both an iPhone 5s and Note 3. Love em both but the Note is a tool for a very specific job I so that uses the SPen to do some amazing stuff that wouldn't be as 'cool' as on graph paper. Other than that, I don't care the app you name, Id it's in parity with iOS, I GUARANTEED iOS runs circles around the Android port. As well the optomized tablet apps are overwhelmingly in favor of iOS, and the biggest challenge with the the Note in different apps I've noticed. They're apps designed for 4.3-4.7" displays and the developers aren't tsking the time to 're-do' their tab apps. They're just blown up leaving a load of white space, sparse UI and pretty lame performance as they're not yet 'coding' to take advantage of multiple core computing. Nearly EVERY app in either environment runs on a single core.
    Mind blowing though you've spent that much time looking at 'blobs' and haven't figured out that IF you TOUCH the 'blob' something really REALLY Cool might just happen!
    Go ahead. You won't break it
    J
    Reply
  • steven75 - Tuesday, September 30, 2014 - link

    Smaller phones tend to be cheaper? The rest cost the same? No, a single part like the display could be cheaper, but there are very real costs to miniaturization.

    Samsung phones not only look cheap because of the plastic, they feel cheap in hand as well. It's not the material--It's what Samsung does with it. Nokia for instance makes some plastic phones that look good and feel great. Samsung comes out with phones that look like band-aids and have fake leather stitching molded into them.
    Reply
  • danbob999 - Tuesday, September 30, 2014 - link

    There you go. Samsung phones are not cheap. You *think* they *feel* cheap. That's your opinion and not based on any fact. Whether a phone is cheap has nothing to do with look or feel.

    And yes, smaller phones ARE cheaper. The iPhone 6 Plus is more expensive to make. The A8 SoC and all other chips are not smaller in the iPhone 6 so there is no additional miniaturization. Only the display and the battery are smaller, and both are cheaper. iFixit teardowns have shown for years that Galaxy S-series are most expensive to make than iPhones.
    Reply
  • mrochester - Tuesday, September 30, 2014 - link

    Doesn't that mean Apple did a good thing? To make a product like the iPhone for less than it costs Samsung to make their Galaxy devices sounds like a big win to me. Reply
  • danbob999 - Tuesday, September 30, 2014 - link

    Of course it is a win for Apple and their shareholders. Not for their customers.
    Of course it is cheaper to put half the RAM, a small display and a small battery.
    Reply
  • bigstrudel - Tuesday, September 30, 2014 - link

    RAM has power costs idiot. It's not worth it just so lazy people don't have to close tabs.

    You must've missed the part where they tested that 1800mah battery and it beat up on devices with 50% more juice.
    Reply
  • danbob999 - Tuesday, September 30, 2014 - link

    I am not saying the iPhone is a bad device.
    But don't call cheap a phone with more expensive components juste because the shell is in plastic. That's all I am saying.
    Reply
  • mrochester - Tuesday, September 30, 2014 - link

    I think the expression was relating to the device feeling cheap in the hand, not the actual BOM. Reply
  • danbob999 - Tuesday, September 30, 2014 - link

    @mrochester
    Is this a tech site or a teenager fashion magazine? Why would anyone care about how cheap it feels in the hand as long as it is a good device?
    A metal enclosure with no electronics in it may not feel cheap in the hand but it would be useless. What matters is inside.
    Reply

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