We spend a lot of time watching and listening to our smartphones and tablets. The younger you are the more likely you are to turn to them for watching a movie or TV show instead of an actual TV. For a lot of us it is our primary source of music with our own content or streaming services. Very rarely when new phones or tablets are announced does a company place any emphasis on the quality of the audio.

Display quality also used to receive very little attention. As more and more people reported on the display performance, more companies started to take notice. Now benefits like “Full sRGB gamut” or “dE < 3” are touted on new products. So now we are going to introduce a new set of testing for smart phones and tablets, audio performance.

To do this right we went to the same company that all the manufacturers go to: Audio Precision. Based out of Beaverton, OR, Audio Precision has been producing the best audio test equipment out there for over 25 years now. From two channel analog roots they now also test multichannel analog, HDMI, Optical, Coaxial, and even Bluetooth. Their products offer resolution that no one else can, which is why you will find them in the test and production rooms of almost any company.

Just recently they introduced a brand new set of audio tests for Android devices. Combined with one of their audio analyzers, it allows us to provide performance measurements beyond what has been possible before. Using an Audio Precision APx582 analyzer we set out to analyze a selection of Android phones to see what performance difference we can find. More phones and tablets will follow as these tests can be run.

The Test Platform

The test platform is the Audio Precision APx series of audio analyzers. For this initial set of tests I used an APx 582 model, which has two analog outputs and 8 channels of analog inputs. The outputs are not necessary as all of the test tones are provided by Audio Precision for playback on the devices. For each set of tests we can add a load, simulated or real, to see how the device handles more demanding headphones. For this article I am sticking with only a set of the updated Apple Earbuds. They are probably the most common headphone out there and easy to acquire to duplicate testing. For future tests the other loads will be AKG K701 headphones and Grado SR60 headphones. Both models are popular, and I happen to own them.

There are a few main tests we are going to use for all these reviews. Those key tests are maximum output level, Total Harmonic Distortion + Noise (THD+N), Frequency Response, Dynamic Range (as defined by AES17), and Crosstalk. These tests are the exact same ones that manufacturers will be running to verify their products. Most of these tests will be run at maximum output levels. Most amplifiers perform best at close to their maximum levels, as the residual noise compared to the signal decreases, and so that is what they are typically tested at.

We might add more tests as we decide they are relevant to our testing. I will also attempt to go back and fill in as much data as possible from previously reviewed devices as time permits. Now to look at the tests and see our results for our initial set of phones.

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  • Impulses - Monday, December 9, 2013 - link

    Ehh, impedance curves for the headphones he suggested (Grado SR80, AKG K701) are easy to find (Inner Fidelity and others have decent databases)... Testing and providing output impedance for the phones would be very valuable indeed though, even if everything else in the chain performs alright that alone can affect the FR significantly with one pair of headphones and not at all with the next... And unfortunately there's never been a realistic standard for output impedance, (other than high quality solid state amps now aiming for >1 ohm), and it's often all over the place.
  • ssddaydream - Monday, December 9, 2013 - link

    I agree with this.
    I think of three main usage scenarios regarding the headphone output:
    1.) Quality of HP output driving a high-impedance line-level input for a home or car stereo.
    2.) Quality of HP output driving low-impedance, sensitive IEMs.
    3.) Quality of HP output driving high-impedance, non-sensitive cans.

    For #2 and #3, the output impedance should be known, as well as the amplifier power at a given THD level.
    There reasons why the iPhones are able to perform well with IEMs, namely low noise floor and low output impedance. Also, iPhones perform well with larger cans because of the decent output power.
    I think the usage cases I listed above are pretty common, so I think a good approach to testing is to think about the most important parameters for each usage case.
    BTW, I am excited about AT doing these measurements- very good news, indeed!
  • Anand_user123 - Monday, December 9, 2013 - link

    I use my phone most of the time as a music player. Audio quality and storage capacity for flac files are major factors in my buying decision. I hope we can have more widespread information on smartphones audio performance
  • stepz - Monday, December 9, 2013 - link

    If you actually cared about scientific measurements of audio performance you would use compressed audio instead of flac. ;) Given a decent amount of bitrate, compressed audio is indistinguishable from uncompressed in double blind tests. In my experience FLAC is mostly about the listener feeling good about getting the "correct" experience, like expensive speaker cables.
  • Impulses - Monday, December 9, 2013 - link

    There's a valid usage case for FLAC as far as ripping and archiving IMO, you might as well if you're ripping a large collection (or ripping often)... Since you can quickly re-transcode or edit files w/o a loss of quality... But yeah, I don't see why anyone would put FLAC files on a phone, transcoding is dead simple and super quick if you have a remotely modern PC. Managing FLAC & MP3 playlists or whatever shouldn't be a hurdle if you're putting the effort to maintain a FLAC library to begin with, just use the MP3 library for everything or use stuff like Media Monkey's smart filters/playlists.
  • NaterGator - Monday, December 9, 2013 - link

    The biasing of the amplifier in the Nexus 5 and LG G2 left channel appears incorrect. Note it is only clipping on the negative portion of the waveform.
  • vshah - Monday, December 9, 2013 - link

    Can't wait to see htc one results!
  • jrs77 - Monday, December 9, 2013 - link

    Could you compare the phones to an iPod maybe? This way we would've an comparisooon to a mediaplayer where there's no 3G/4G/LTE disturbance.

    Oh, and for the general audience discussing the DACs etc... The DAC isn't the cruicial part, never has been. The amp is what it's all about and how good or poor it's powered.
    There's a reason why audiophiles still use tube-amps, or atleast digital amps with high quality toroidal transformers and good shielding to reduce noise distortion etc.

    Oh, and btw... A good mediaplayer needs a microSDHC-slot or the possibility to use an USB-stick. A mediaplyer is no good if I can't carry my whole music-library with it (100+ GB).
  • Leezhunjin - Monday, December 9, 2013 - link

    Hi Chris, very nice to see smartphones getting measured in terms of audio performance, as many of these phones are used as a music device as well. Personally, I think that an inclusion of output impedance measurements would really great be though, as it is one of the factors that would affect the earphone performance rather significantly.
  • CSMR - Monday, December 9, 2013 - link

    Very good start. Poor quality needs to be exposed and you've done this with the Nexus 5.
    I would like to see output impedance since low output impedance is a very important quality of a good headphone output.

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