Smartphone Audio Testing - HTC One M8 and Samsung Galaxy S5

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.