Maximum Level

The maximum output level is derived from the 1kHz test tone used to determine THD+N. The higher the output from the headphone jack, the louder it can drive a pair of headphones. More importantly, having more power available means when you have dynamic music passages that call for power you are less likely to clip the waveform.

There is no chart to show here, just a number that the Audio Precision gives us. In our test data, the most powerful phone was the iPhone 5, at 32.46 mW of power. Next is the Nexus 5 at 22.24 mW, though we can’t drive it that high. Then the Note 3 at 11.81 mW and finally the Galaxy S4 at 3.895 mW. Doubling the power, from 4 mW to 8 mW, produces a 3 dB increase in volume level. 3 dB is the smallest change in volume levels we can easily hear. So even though the iPhone 5 produces 32 mW vs. 4 mW, that is only a 9 dB difference in volume. 10 dB is doubling the volume, so it isn’t even twice as loud. If you have demanding headphones, you will want as much power as you can get.

Frequency Response

To measure the frequency response we measure a set of 61 tones from 20 Hz to 20 kHz. All of these are then equalized to 1 kHz so we can see the maximum deviation from that level. An ideal phone will be perfectly flat here and allow you to adjust this with an EQ setting, or though your taste in headphones. On this test our best performing phone is the Galaxy S4, as seen here.

The total variation from 1 kHz is only 0.014 dB which is very good. The worst performing phone is the iPhone 5, but its variation is only 0.089 dB.

The iPhone 5 also picked up the 20 kHz tone while the Samsung and many others missed it. If we dropped this tone then it might be just as flat. The iPhone 5 test was run slightly differently, as it can't run the Android test program, which might account for this. For a phone with a different response, here is the HTC One with Beats enabled. Other HTC One testing is still in progress as I write this article.

Here we see that Beats is adding a +3.5 dB boost from 60 Hz to 90 Hz, but the deviation from 0 dB goes from 30Hz to 300 Hz. Past 6.5 kHz we also see a rise in the treble. People often mistake boosted treble for extra detail, which is likely the reasoning behind this. As we see it is far different than the other two examples we looked at.

THD+N Dynamic Range, Crosstalk, and Stepped Response
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  • Impulses - Wednesday, August 13, 2014 - link

    It wouldn't really be a factor, the Bluetooth device's amp would be what's driving your headphones, not the phone's circuitry.
  • blade 7 - Monday, February 17, 2014 - link

    while quality of music playback is certainly a major issue, one primary quality question hardly gets any mention, not to speak of objective examination: the quality of the phone call audio itself !
    it you conduct crucial negotations over the phone - or even if you just flirt with someone on you portable, the quality of voice call transmission can make a huge difference in how you - your message, business proposition, etc - are perceived on the other end of the call, and what impression yout gain from someone calling you. so where in the respective media is a systematic phone-call audio quality assessment ? ( and no, phone call audio quality is not equal to music file playback audio on a smartphone. we are talking much more elements of the phone involved and influencing phone call audio qu. compared to file playback quality.) a lot of modern smartphones sound very poor on voice calls ....
  • Excerpt - Wednesday, February 26, 2014 - link

    Represent RIP city main! You did an amazing and scientific report I have high hopes for future articles and I'm really behind your trailblazing (another reference) the audio quality topic on our electronics!

    I did a wedding gig with a decent firewire audio interface, ran out of music (as the crowd wanted more current hip-hop) Hooked up my friends iphone and I was a little awestruck. My speaker amp was at about 80% and the iphone 5 was at about 90% volume and the distortion and quality did not seem to dip down at any noticeable amount, through the head phones or the floor speakers. WOW.

    I personally just bought the nexus 5 and yes, even at low levels being hooked up to my home stereo (which i do often) the quality and total max dBs are defiencent compared to the iphone. Crap-tastic infact, the left and right speakers even seem noticably out of phase or somehting to that effect. (I'll start using the S.O.'s ipad air if i need an emergency audio source in the future)

    Just verifiying this man's findings with real world examples. Thanks!
  • Excerpt - Wednesday, February 26, 2014 - link

    Good point and I think there's some information to be discovered on that topic. However, I wanted to add, carriers are really responsible for increasing the quality of voice. The local recording of a mobile device is much better than the transmitted voice (not withstanding software enhancements eg. noise canceling). Check out, 3GPP and the ITU (International Telecommunications Union). There's some benchmarks that are measuring voice quality calls, but assisted with network simulators, as the network is also an important factor.
  • @paulkind3d - Thursday, March 6, 2014 - link

    Call and sound quality are a huge part of mobile phone tech. I'm currently looking into the HTC One as it appears to have set a precedent on sound quality. Personally I am absolutely sick and tired of having to ask "huh, what?" over phone calls due to the crappy little garbage speakers in most cellphones. They are either a) loud enough to hear but are not clear or b) too quiet to hear and are not clear either. Either way hearing calls on cellphones is painful and difficult on every cell phone ive owned to date. I can live with a bulky cell phone if it means better sound personally. Sadly no one else thinks this way. Apparently till a phone is the size of a thumbnail and useless for calling people cellphones makers will not be satisfied.

    I know that this test does not compare that and is more of a DAC question as the test is geared to headphone sound quality (bonus that one of the test subjects is a grado headphone... grados are amazing... i love my sr325's). None the less, the fact that someone is out there testing audio quality of cell phones means that eventually we may be able to actually hear phone calls when we make/answer.

    BTW has many user posts on this same subject. If line level quality is important to you definitely search headfi too. This and many other compares can be found there...
  • H0rtOn - Thursday, May 8, 2014 - link

    I read Anandtech alot and have never posted a comment before, but I signed up just to make this post. Please make this a standard part of your phone reviews. I specially missed this part in the review of the HTC One (M8).
  • notsure123 - Friday, April 29, 2016 - link

    Old article. I would just like to point out the difference between driving apple headphones (or any headphones for that matter) vs a line input. Not to say this data is inaccurate, it is just not particularly useful in comparing smartphones audio quality. Firstly because I hope no one actually uses their smartphone with headphones at volumes even up to 80% where it might also start distorting. This is too loud and is damaging your hearing. I would like to see the distortion figures when connecting the headphone jack to an auxiliary input rather than a headphone and see how these phones compare (willing to bet its much more similar)
  • Photosynthecis Media - Friday, March 6, 2020 - link

    It is important here to differentiate between the microphone and the rest of the audio system if you will because if the microphone is providing the input then its intrinsic response curve will apply kind of like a coefficient to what the audiio sys output is. Whereas an aux input other than the microphone would offer an output only affected by the frequency response characteristics of the amplification system, primarily the speakers, but not the microphones.

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