HTC One M8 Audio Testing

Looking at the numbers for the HTC One M8 there are a few things that stand out. The first is the output power of around 1.2 Vrms for all loads. This is a lot of power for a smartphone and should be able to drive almost any set of headphones you would use with it. There is more distortion on the 15 Ohm load but as there are 95 mW at max volume, you should be able to step the volume down a bit and reduce the THD+N.

We also see that crosstalk gets better as we have an easier load to drive. The lower (more negative) the crosstalk is, the less noise is leaking from one channel into the other. This is also the test most subject to error when using the USB automation of the phones. On the HTC One M8, USB testing results in a crosstalk level of -0.01 dB. If you are using your HTC One M8 for music you are best to not have it connected over USB while listening.

  15 Ohm 33 Ohm 150 Ohm 330 Ohm
Dynamic Range 91.791 dB 92.074 dB 91.690 dB 92.008 dB
THD+N 0.3365% 0.0152% 0.0103% 0.0101%
Crosstalk (L) -58.032 dB -64.780 dB -77.688 dB -83.656 dB
Crosstalk (R) -57.950 dB -64.329 dB -77.194 dB -83.240 dB
Output Power 95.55 mW 47.63 mW 11.14 mW 5.116 mW
Output Voltage 1.197 Vrms 1.254 Vrms 1.293 vRMS 1.299 Vrms
Relative Level (20Hz - 20kHz) ±0.664 dB ±0.664 dB ±0.665 dB ±0.665 dB

For some of the other results, I am going to pull in some charts that help to explain it better.

Relative level shows it is flat until the 20 kHz tone. Since most people can’t even hear this, the fall off there isn’t a large deal. The fall-off at 20Hz, which most earbuds cannot produce to a reasonable level, is much more slight and not audible. Unless you are playing back music for your puppy with the HTC One M8, this result is fine but it could be better.

THD+N is below 0.03% until just after 2 kHz when it begins a slow rise up past 0.2% at 20 kHz. This winds up being a good number but I am unsure what causes the rise in THD+N as the frequency increases.

The FFT spectrum for the 997 Hz test tone shows all artifacts below -80dB compared to the fundamental. The second and third harmonics are the largest, and those drop off by -10dB by the 4th and 5th.

This graph compares the frequency response to the BoomSound feature to having it disabled. As we saw earlier the regular frequency response is flat with a steep fall close to 20 kHz. Looking at BoomSound we see a steep roll-off below 30 Hz, a peak of almost +5dB around 60 Hz, a -5 dB section between 200 Hz and 500 Hz, and then a steep rise in the treble past 2 kHz.

Since I didn’t do the subjective listening, I would expect this to sound harsh in the treble, with the midrange being washed out by that dip in the middle. What we have is a high-end and a low-end that is +10 dB compared to the midrange. So these will sound twice as loud to you as the midrange. Using the interactive chart of music instruments by frequency you can find here, you can see what instruments this will obscure.

Comparing the THD+N ratio of BoomSound On to Off shows far more noise and distortion as well. If you want boomy bass, a harsh top-end, and no midrange, then use BoomSound. A better choice is to find headphones that suit your listening preferences more.

The HTC One M8 has good looking numbers, but putting them into better perspective requires more phone testing. As it is I see nothing that stands out as being a problem, unless you leave BoomSound on.


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  • CSMR - Tuesday, June 3, 2014 - link

    I would also like to see output impedance.
    Especially as the tests now use dummy loads, which will mask the effect of high output impedence on frequency response.
  • Doroga - Tuesday, June 3, 2014 - link

    Yes, would like that one for both phones and motherboards reviews (at least 1 midrange board per brand to get an idea).
  • pelms - Tuesday, June 3, 2014 - link

    Very interesting. I'm hoping phone manufacturers will come to treat audio quality with the attention they (and the press) pay to camera quality.
    It would be interesting to test the iPod Classic and Touch to get a baseline for comparison.
  • Jimster480 - Tuesday, June 10, 2014 - link

    Well I have a first Gen iPod touch with a Wolfson and I have to say there is a night and day difference to the M8. It sounds better with all forms of sound. Its alot clearer and the sound stage is alot deeper.
  • Anakha - Tuesday, June 3, 2014 - link

    Nice article! :) One question, do you feel like voiding your warranty and converting the M8 to the Harmon/Kardon version? The details for the conversion can be found here: I am curious to see if this would make any difference?
  • jk1 - Tuesday, June 3, 2014 - link

    thank you for this article. i would really like to see an evaluation of audio become part of every anandtech smartphone review - both as a music source and for telephone. these phones are routinely used as music sources, but that function is typically neglected in favor of exhaustive analysis of the cameras.

    if you do decide to do evaluation of dedicated portable audio sources, let me nominate the ibasso devices - dx50 and dx90, as well as the fiio's- x3 and x5. these receive the most discussion over at head-fi, so i'm sure there would be interest.

    btw- although i check anandtech's smartphone page regularly, i actually came to this article through a link posted in a thread at head-fi, a thread devoted to the htc one m8 as an audio source. i'm sure more audio reviews will generate more links, there and elsewhere.
  • Jodiuh - Tuesday, June 3, 2014 - link

    Thank you AT, I knew this already, but wanted confirmation. Can this thing power some AKG Q701's?
  • synaesthetic - Saturday, June 7, 2014 - link

    Not very well.
  • Zoomer - Tuesday, June 3, 2014 - link

    Testing more phones will be helpful! One M7, Nexus 5/7/10, Xperias, the Apples.
  • The1Metallian - Tuesday, June 3, 2014 - link

    Thanks for the article! Now - is there a test of the quality through Bluetooth? I hear all my music on my GS3 through the sound system in my car via Bluetooth and I've noticed that music sounds better when coming from my wife's iPhone. I am now evaluating a phone upgrade and music sound quality is high in my consideration, but always staying with Android.

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