THD+N is a measure of the total harmonic distortion and noise compared to the signal. The lower the number, the less distortion and noise there is relative to the fundamental frequency. THD+N is measured by driving a 1 kHz sine wave at maximum volume. Because there is always some inherent background noise, the THD+N is almost always lowest at maximum output so that is used for the measurement.

There are two results that we take from this: a sine wave and a FFT spectrum. On the sine wave both channels should line up perfectly, and it should be as close to an accurate sine wave as possible. On the FFT we want to see a peak at 1 kHz and everything else as low as possible. The most common artifact you will see are harmonic sidebands at multiples of 1 kHz.

For an example of data that looks good, here is the sine wave of the iPhone 5. We see a sine wave that is good, with channels that overlap perfectly and no deviation. This is what we expect to see.

Now for a different example we look at the Nexus 5. Run at maximum volume we see that the left channel is clipping in the sine wave. Likely the power to the headphone amplifier is not enough to drive both channels and so this is the result. UPDATE: Tested this with 4.4.1 and no change.


The iPhone 5 produces a THD+N ratio of 0.003134% while because of the clipping, the Nexus 5 is producing 13.789197%. Any level over 1% is considered to be past the clipping point of an amplifier and it seems that the Nexus 5 cannot be driven at maximum volume. I tested two samples to verify, and on both the performance is identical.

Now if we look at the FFT for this test, we see how this distortion is showing up. First, the iPhone 5 is very quiet.

There is a 2 kHz peak that is -93 dB below the fundamental frequency, and the 3rd harmonic at 3 kHz is over -109 dB below it. All the harmonics past that are at -120 dB below the fundamental tone. There is some noise out at 50 kHz but this is so far past the level of human hearing that it is safely ignored. Now the Nexus 5 FFT.

We see the right channel, which didn’t clip, looks good. The 2nd harmonic is -111 dB and the 3rd harmonic is -93 dB. On the left channel the 2nd harmonic is only -18 dB and the 3rd harmonic is -24 dB. Even at the 9th harmonic we are still only -52 dB below the fundamental tone. This is causing these incredibly high THD+N numbers that we are seeing on the Nexus 5. We will see more detail of this on a later test as well.

We also chart THD+N vs. Frequency. Here is the chart for the Note 3.

We see that THD+N is basically right below 0.08% for the whole spectrum. It moves up and down slightly, but is very constant. Now here is that Nexus 5 data.

We see that the right channel is around 0.01% THD+N while the left channel, the clipped one, is over 3%. If we ran the Nexus 5 at a lower volume level we would see totally different results, as you’ll find out later, but this is how devices are typically measured.

The Test Platform Maximum Level and Frequency Response
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  • sonci - Friday, December 13, 2013 - link

    Thanks Anandtech,
    Nice for doing these reviews, one of my top reasons for choosing a smartphone is audio quality, and im not talking about the voice of my wife, but the music reproduced through earbuds.
    Please keep going testing at full volume not only for those who use them with an external integrated, but because that's the right way, if manufactures bost the volume and allow clipping than thats a flaw, also if a phone measure good at full volume than its super good at low volumes, you also can measure them at a specific sound pressure levels, though the difference should be small, but anyway these are not reviews for the casual listener,
    and Yes unfourtunately iphones sound very good.
    I also would be interested in measuring some old and new mp3 players, though in that case its different to be objective, because for a n audio player SQ is a major selling point, but I dont see Lumia selling more than Galaxie because of better SQ.
    If you cant find any old mp3 player, we are crazy enough to send them to you, hoping to have them back once tested.
  • Mokona512 - Saturday, December 14, 2013 - link

    Can you do a comparison of smartphones and dedicated mp3 players?

    for example my sandisk sansa running rockbox firmare gives much better audio quality than my smartphone, especially when driving my akg k240.
  • cb474 - Saturday, December 14, 2013 - link

    I appreciate the sophistication and thoroughness of this review. But I have to say that I have never had a smartphone where I've thought, boy this audio quality is unacceptable. Especially with earbuds or plugged into an external system. Unless you're an audiophile, they all seem pretty good to me.

    Speakers on smartphones are obviously another story.

    But to me the real issue is call quality, including earpiece volume, sound quality of the mic (for one's caller), and especially noise cancellation. Anandtech, thankfully, covers noise cancellation in its reviews with a meaningful babble track test. But I wish there were still much more focus on call quality. There are real differences when it comes to call quality, even amongst flagship phones, and this is an area in which, on a daily basis, I experience frustration. It's amazing how much the "phone" functionality of something that is after all phone is ignored.
  • kevmitch - Sunday, December 15, 2013 - link

    I agree. Excellent article. I hope to see more like it and on the subject.

    I wouldn't mind the "sensational" scales so much if they were at least used consistently. It was difficult to compare for example the THD FFT responses by tabbing between them in browser windows because the scales aren't the same.

    While the max volume should really be set correctly, it would nevertheless be interesting to see the THD FFT for what SHOULD have been the max volume (i.e., a step or two below the G2). I have to say I'm a lot less excited about getting a Nexus 5 now - the Galaxy 4 looks much more appealing in spite of the significant price increase. These results even had me consider getting an iPhone for about half a second.
  • vang024 - Monday, December 16, 2013 - link

    Sorry, but shouldn't you be using lower impedance headphones? The grado is rated at 32 ohms and the K 701 is rated at 64 ohms. The grado might be ok for portable electronics use but the K 701 is more difficult to drive than the 64ohms it is rated at. Not only that, but they are both open headphones which leaks tons of sound and not prefer for anybody using a portable electronic as their music source.

    I think you have to inform the reader the difference between a closed and open headphones(assume they don't know the difference). I see people purchasing a HD600/650 or an AKG Q702 and complains about the sound leakage when these headphones are design to do so. Most of the time people will purchase headphones like a B&W P5/P7, KEF M500, Bose, or Beats for portable use because they are closed design with low impedance. I would say those are targeted for smartphone users.

    I am not saying you shouldn't test smartphone devices with higher impedance headphones, but The Grado and AKGs are not designed for the average joe who don't know much about headphone technologies.
  • bogdan.anghel - Thursday, December 19, 2013 - link

    i listen to a lot of music on headphones, i own a S3, and i want to upgrade to S4 and everywhere i see a review the audio quality and power is very bad. should i go with the HTC One? audio and design is very important to me. (i love the S4 but in terms of audio and design, it's crappy) do any of you guys test or compare those 2 on the same headphones?
  • manveruppd - Friday, December 20, 2013 - link

    It's great to see you pushing the boundaries of phone reviewing by testing things that noone else bothers to, and with a scientific precision no one else can match, but i do have a couple of suggestions:
    firstly, how about also testing the quality of the built in speakers, rather than just the headphone amp? after all, sound qquality in calls is an important consideration when buying a phone. as for the loudspeaker, while i agree that noone except annoying teenagers would listen to music through their phone's loudspeaker, a lot of people use the speakerphone function on their phones regularly, so it's a legitimate area of testing.
    secondly, i wonder if it's fair to test all phones with a set of ear buds designed for one phone? if i were a manufacturer i would make sure to bundle a set of buds that sound good driven by the headphone amp i built into my phone, and i would expect it not to do as well with a higher impendance pair of headphones,for example. so to test on apple buds is probably not quite fair on other devices. i would simply pick 3 pairs of headphones, one each of high, low, and medium impendance, made by some reputable audio brand rather than by the manufacturrer of one of the tested devices.
    good job though, looking forward to future review
  • synaesthetic - Thursday, December 26, 2013 - link

    output impedance please!
  • seshraj - Wednesday, January 1, 2014 - link

    Thanks for another wonderful post.

    One suggestion to include one Xperia smartphone in your list to test. I personally use an discontinued model Arc S for close to 3 years now and have always been pleased with the bravia audio quality and output, sunlight visibility and camera. I am not a techie or a heavy user of a smartphone; but amazed with the audio quality of this device. I am sure the newer models like Xperia Z would have a more upgraded and better sound quality.
  • jcazes - Tuesday, January 7, 2014 - link

    Can anyone comment on how these deficiencies translate to A2DP streaming over bluetooth? I have an LG G2 and am looking at finding something with Apt-X / aptX support (or cooking it in via a custom ROM, if possible). If the phone can't output audio properly over any channel then I don't want to waste my time.

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