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 - Wednesday, June 4, 2014 - link

    It doesn't matter if they're using the same DAC. They provide no line-out functionality so you're subject to the limitations of the amplifier driving the headphone jack. In this case, the amplifier that HTC has chosen to use is far more powerful, with less noise and crosstalk, than the one that Samsung chose. It's impossible to isolate a single component, like the DAC, and expect everything that uses it to have identical performance. It's part of a system and everything else in the system has to perform at a level for it to function right.

    For the subjective testing, I'll leave that to Anand and Joshua who are spending far more hands-on time with the phones than I am. I'll run the numbers and provide a straight analysis of them.
  • theduckofdeath - Thursday, June 5, 2014 - link

    The reason they need subjective listening is because they insist on using hyperbole to differentiate devices. Based on data output from a metering device.

    Here's an example why actual human testing is needed:

    Lambasting something as horribly bad without actually making a real life comparison is a typical nerd error. "The numbers are superior, therefore it must sound superior!". The human ear is really limited in what sounds it can pick up. It's not nearly as accurate as Chris appears to think as very few adults, especially those who frequently listen to headphone music, can hear anything even near 20kHz.
  • synaesthetic - Saturday, June 7, 2014 - link

    Sighted listening produces biased results. Measurements are verifiable, demonstrable and repeatable. Subjective listening tests are just that, subjective and thus useless to anyone but the person doing the listening.

    This is why I appreciate actual data. I can look at a frequency response graph for a headphone and compare it to another headphone I know I like, and I can get an idea how the other headphone sounds without having to decide which subjective listener's ears I'm going to trust.
  • theduckofdeath - Wednesday, June 11, 2014 - link

    The point I made is, measuring things that are probably not even audible to a human being ,and use that as a review for audio quality is pretty pointless. Then you've really missed the whole point of being a product review site for devices intended for regular human use. :)
  • apertotes - Tuesday, June 10, 2014 - link

    but you did not answer. Which Galaxy S5 did you test?
  • Jimster480 - Tuesday, June 10, 2014 - link

    The M8 sounds alot better than the GS5. Its been determined so many different times. I own an M8 aswell and I have to say the sound quality is like none other.
  • edzieba - Tuesday, June 3, 2014 - link

    I'd like to see Output Impedance measurements. If that heads north of 2ohm, then that's a good red flag for things having gone seriously wrong.
  • Rezurecta - Tuesday, June 3, 2014 - link

    No it is not. Where did you get this misinformation?
  • synaesthetic - Saturday, June 7, 2014 - link

    Output impedance is THE single most important factor for how a given driver will sound with a given analog output. When the 1/8th Rule is violated, the driver will lose some or all of its electrical dampening. This usually tends to kill bass and warp the rest of the headphone's frequency response, making it sound abnormal.

    The fact that most manufacturers, reviewers and the like never bother to check output impedance is very, very annoying and makes headphone selection needlessly complicated. Very low-impedance headphones, such as Ultimate Ears IEMs, will not sound "normal" out of a source with an output impedance over 1.6 ohms.

    Properly designed amplifier sections should have an output impedance as close to zero as possible so that they work properly with all headphones.
  • Jimster480 - Tuesday, June 10, 2014 - link

    Well my M8 has worked fine with 5 different headphones I have tried it with. 3 Different sets of IEM's (Sony Earbuds, Skullcandy IEM's, and Bose IEM's). And a Sony over the ear aswell as a Panasonic RP-HT360 and it sounds very clear and rich on every set. No set is too loud nor does the sound reproduction sound incorrect or flawed.

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