Smartphone Audio Quality Testing
by Chris Heinonen on December 8, 2013 5:15 PM EST- Posted in
- Smartphones
- Audio
- Mobile
- Tablets
- Testing
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.
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psuedonymous - Monday, December 9, 2013 - link
Any chance of a test/roundup of bluetooth receivers?Impulses - Monday, December 9, 2013 - link
I'd love to see that.deathdemon89 - Monday, December 9, 2013 - link
I do hope you consider providing the audio tests in the main review on the day it's published, as opposed to tacking it on later. I usually read reviews only once, i.e. on the day they are published and don't keep returning to individual reviews looking for updates, so this would be a major data point readers like me would not be able to take advantage of.DanNeely - Monday, December 9, 2013 - link
I wouldn't hold my breath. Chris H isn't a typical smartphone reviewer. As a result getting these results at initial launch time would require either buying additional sets of test equipment for the reviewers, buying an additional phone for Chris H to do audio testing on, or delaying the article to ship the phone to Chris H after completing the rest of the testing work.Audio precision won't let you see pricing information without creating an account on their website. That suggests it's painfully expensive and that getting multiple copies of the hardware won't happen. Getting multiple copies of the phone isn't cheap either and is probably not going to happen except perhaps for a few halo devices. With the peanut gallery raging about any reviews that don't make it out on release day, I'm doubtful that anandtech would choose to delay reviews for a few days for a specialized test.
Impulses - Monday, December 9, 2013 - link
Ehh, I agree, if it's not realistic to have this testing the day the review is out it's no big deal... If it's a deal breaker for you then you'd wait the same amount of time either way, and if it's not (probably the majority of readers) then there's no point in making the rest wait.xaml - Saturday, December 14, 2013 - link
"Chris H isn't a typical smartphone reviewer. As a result getting these results at initial launch time would require either buying additional sets of test equipment for the reviewers, buying an additional phone for Chris H to do audio testing on, or delaying the article to ship the phone to Chris H after completing the rest of the testing work."Or buying an additional Chris H...
cheinonen - Monday, December 9, 2013 - link
Having this on the day-of is going to be a challenge for a number of reasons.- Brian is in Arizona, and I'm in Oregon. If there is only a single review sample, I have to get it from him.
- As mentioned, the Audio Precision is ridiculously expensive. I think the APx 582 used starts at $19,000 before adding the HDMI, Bluetooth, and Digital modules I use (I need it for receivers as well). Audio Precision is just a few minutes from my house and they've been nice enough to let me come in, test everything there, and endlessly bother their QA people to get this right. However, as I have to come in I have to schedule that, and it takes time.
- That also makes it far easier to do a batch of these at a time than one at a time. If I had at APx at home it would be easier but right now that's not possible.
So we will try to get all the data, as fast as possible, into the system, but day-of is going to be a logistical challenge. I'd rather have it be accurate than be fast.
cheinonen - Thursday, December 12, 2013 - link
OK, I shouldn't say ridiculously expensive. However, the instrument we use costs enough that it's not feasible for us to have them for myself, Anand, Brian, and everyone else that needs one for testing. The Audio Precision gear ranges from $6K to $50K+ depending on what you need and the price still means we can't outfit everyone with one. So testing will happen as fast as possible, but likely won't run with the reviews when they are initially posted.Bobs_Your_Uncle - Monday, December 9, 2013 - link
This audio bench is a tool of truly significant value to anyone hoping to arrive at the best, most fully informed purchasing decision possible. Given the respect & high regard that AT has earned throughout the tech sector, this audio initiative raises the bar for more than smartphone manufacturers alone.Along these lines, does AT have any plans to initiate a similar audio bench for the various motherboard lines that have recently implemented enhanced audio capabilities?
These are very positive steps toward driving advances in fundamental, yet long neglected platform capabilities. However, as improvements in audio reproduction are realized, there will still remain one critical, & seemingly intractable obstacle to overcome; What's it going to take for the recording industry to give up on compression & adopt a regimen of decent mastering.?
It'd be a shame if the only thing audiophile-grade tech revealed was just how badly most studios butcher great music through compression & lousy mastering.
Impulses - Monday, December 9, 2013 - link
I think that battle's beyond Anandtech'srealm, though the more cognizant the average reader/listener is the better.