Since our initial turn in testing smartphone audio, I’ve had a lot more time to play with the APx582 from Audio Precision. I’ve also received far more feedback than I ever expected to on this subject. I have made a few changes to the testing method that I’m going to outline along with discussing some of the reasoning behind the changes.

All tests are now run manually instead of automated over USB

For most phones, running over USB and running them manually provide the same results. For a few, the commands sent with adb to adjust volume result in a higher maximum volume than you can select with the volume buttons. This causes results that are not correct for real-world use.

Note that non-Android phone testing will be identical. The test tones can be manually selected and used regardless of platform. I will try to determine why this happens, as there is the potential for other software to also set the volume control too high. I’m most concerned with results that match real-world usage and this does that better.

Using standard dummy loads

Before I used common headphones (Apple earbuds, Grado SR60s, and AKG K701s) as my loads. While more real-world than resistors, they also present more issues. They have a nominal impedance, but their impedance might be low in the bass and high in the midrange. If you only base results off the nominal impedance numbers, you can mis-interpret charts.

Duplicating the results also becomes a challenge. The parts used in headphones can change during production. Someone trying to match up their results to ours may not be able to achieve the same data with what they believe are the same headphones. A resistor has a tolerance as well, but with fewer variables it is easier to interpret the data and replicate the results.

For the dummy loads, I selected 15 Ohm, 33 Ohm, 150 Ohm, and 330 Ohm loads. During testing I load each channel with the same value of resistor. The Audio Precision software calculates the wattage from the resistor and voltage.

Fewer charts

The standard Audio Precision smartphone project produces lots of charts. Seriously: a lot of charts. It is easy to include every chart in there but most often they aren’t needed. Instead I plan to summarize the data into a nice table form and include the charts that are indicative of performance. If a chart shows nothing new or unusual, I likely will not include it. If a new chart helps to explain what is going on, I will include it. So sometimes you will see a chart and sometimes you won’t depending on what it shows.

I will pull almost all charts from the 33 Ohm loads. This is the the closest to real-world earbuds for most people. There are a lot of earbuds that drop down into the 16 ohm range, and you should look at the 15 Ohm results for those. Since this is a harder load to drive you are most likely to see worse results than with easier loads. People using over-ear headphones with impedances in the 150-300 Ohm range should use those results. This is easier to drive, but also is going to output far less power in watts so you need to pay more attention to those numbers.

This first round-up includes the HTC One M8 and the Samsung Galaxy S5. This is also purely objective listening. My time with the phones is usually short and I don’t have the time to offer my subjective opinion on the audio quality. I will leave that up to the original reviewer.

HTC One M8 Audio Testing
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  • cheinonen - Tuesday, June 3, 2014 - link

    Measuring jitter would require these to have a discrete line out. Any jitter present off the DAC is being masked by the noise from the amplifier and cannot be reliably measured. Jitter would likely be falling around -110dB or below, but that would be swallowed up by the noise floor here. Reply
  • edzieba - Tuesday, June 3, 2014 - link

    What /about/ jitter? Unless your equipment is seriously faulty, jitter is a non-issue. It's the "this is TOTALLY why you need to spend more on our magic cables than on your equipment!" for the digial age.

    You can feed SPDIF over a coathanger (https://web.archive.org/web/20010419223607/http://... and experience no jitter issues (or any other issues).

    When outputting an analog signal (i.e. the amplified headphone out), jitter is a total non-issue.
    Reply
  • althaz - Tuesday, June 3, 2014 - link

    I'd also love to see a test of the Lumia Icon or the 1020. I haven't heard them, but the 920 at least doesn't sound as good as the iPhone or the HTC you've tested above. Wouldn't switch OS for a better sound, but would buy a newer phone. Reply
  • willis936 - Tuesday, June 3, 2014 - link

    One thing that I think is important here that is rarely measured is the amount of noise from the radios that gets rectified in the amp. We've all heard the characteristic tick tick tick from when we laid our phone next to the stereo. Some phones are better than others in terms of not having audio affected by the phone's radios. Reply
  • name99 - Tuesday, June 3, 2014 - link

    That was a feature of GSM and the particular way it timesliced. It didn't occur with CDMA devices, and it shouldn't occur with any modern phone that's using WCDMA, HSPA, or LTE. Reply
  • DoctorG - Tuesday, June 3, 2014 - link

    I get radio noise all the time with my CDMA Galaxy Nexus (and Palm Pre before that.) Reply
  • willis936 - Tuesday, June 3, 2014 - link

    I get it loud and clear from my razr (XT912) when I put it near headphone amp or stereo that my computer uses. I'm also moving to an HTC One (M7 Verizon) and it too has the issue. I haven't tried turning off CDMA altogether but since I have LTE coverage and the noise only comes when there's data usage I'm going to conclude it's the LTE. They can do clever shielding and filtering tricks to keep it from affecting the amp inside the phone. You literally can't do anything besides keep it in your pocket to avoid the noise in other amps. A faraday cage at 700 MHz is nearly air tight. Reply
  • Jimster480 - Tuesday, June 10, 2014 - link

    On my M8 I haven't noticed the audio being affected by the radio. Actually all 3 of my HTC's (HTC EVO 4G, EVO 4G LTE, One M8) haven't had this issue. They do have a bit of feedback if plugged into the charger and the battery percentage is high. But other than that their sound has been pretty pure, and better from generation to generation! Reply
  • Ammar666 - Tuesday, June 3, 2014 - link

    Which Galaxy S5 did you test? The Qualcomm one or the Exynos one. Because the Exynos one comes with a Wolfson DAC I think. Reply
  • theduckofdeath - Wednesday, June 4, 2014 - link

    I would have guessed they tested the common Snapdragon based one. But then again, that one uses the same DAC as HTC as far as I know which would mean that either the test is flawed or Samsung screwed up the software on the GS5. I remember it was the complete opposite with last years generation, where the GS4 had much cleaner sound than the old "One", even though those two also used the same DAC. (according to measurements done by GMS Arena)

    Personally, I'm not a big fan of these type of pure technical test to find the best sounding device. You need some sort of human tap-in, like an extensive blind-test, to get a real life reference as to where they really stand. Especially when you use hyperbole to the extreme like Mr. Heinonen is.
    Reply

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