Frequency Response (9.67) 
Our first audio performance test looks at the frequency response of the media player; how well it plays back the many frequencies that music contains. To do this, we play back a special sound that contains the whole range of frequencies, and our testing system listens to the output on the headphone socket of the player, and determines how loud each of the frequencies is. It them produces this graph below, which shows the frequency range, from very low (at the left), to very high (at the right. The ideal here is a flat response, meaning that the player plays back all frequencies at an equal volume.
The new iPod Nano 6th Generation did extremely well in this test; the frequency response curve is very flat, with only a minor bump at the very high end. And this bump is very minor; most people are not even going to notice this. Overall, the iPod Nano has excellent frequency response with no bumps or dips, playing back every frequency almost identically.
One thing to note here is that we test with the equalizer feature of the player turned off; this works by changing the frequency response to suit the type of music being played.
Distortion (9.43)
Distortion is the curse of the media player; it happens when the sound comes out differently from the way it was recorded. It cna happen for a number of reasons, including cheap amplifier chips inside the player or if the player does a poor job of decoding the recorded music. Again, we test it by playing back a special sound while the testing system monitors the output, looking for any differences between the sound and the output.
Distortion did not seem to be an issue with the iPod Nano; we found that the amount of distortion present at the headphone output was extremely low; our system could barely detect any at all, even with the volume control set at maximum. However, it is worth noting that the headphones that come with the iPod add another level here; we found that they add a significant amount of distortion to the signal (see below).
Cross Talk (8.84)
If your favorite song has your heartthrob crooner whispering sweet nothings into your left ear, that's where he needs to stay; you shouldn't hear him in the other ear. If he is in both, that's called cross talk, where a signal that should only appear in one channel (the left or right headphone output) ends up in both. It happens on some media players because the two channels share some components and the system gets confused, but it wasn't an issue with the iPod Nano; we found that the amount of sound that leaked from one channel to the other was very, very small; the ratio was 104 decibels, which puts it well below the range of human hearing. So, your crooner will stay firmly where he should be with the iPod Nano.
Output Power (7.26)
Another major factor for media players is how much power they output. The more power they output, the better the job they can do at driving bigger pairs of headphones. A poor media player might only output 10 or 20 milliwatts of power, which means that it would not have the juice to drive a better set of headphones than the one they come with, limiting your options to add bigger and better headphones to replace the ones they come with. We measured the output power of the iPod Nano at 29.1 milliwatts, which is decent and enough to drive most headphones; this is enough for most in-ear and earbud style headphones. However, it will begin to choke if you try and use a very large or a particularly high impedence set of headphones; the sound will be low in volume, and it may sound overly distorted and grungy. So, the iPod Nano is fine for most earbud and in-ear type headphones, but it will have problems if you prefer a set of bigger, over hear headphones or want to use a set of professional cans; many of these will have a higher impedence and may have some issues.
Noise (9.84)
Noise is the slight hissing that you hear in quiet pieces of music that spoils the effect. We test this by looking at how much noise we can detect when playing back a special file; we found that the iPod Nano had very low noise. We measured the ratio of the signal in the file to the noise at around 92.99 decibels, which means that the noise is very, very low (a higher number here indicates less noise). So, the amplifier and playback parts of the iPod Nano don't add much noise to the sound that they play back.
Oen thing to note here; the noise we test is the noise that is produced by the media player, which is different than the distortion caused by a poorly compressed file. If you compress your files down to a particularly small size, your music will contain lots of distortion that can sound like noise. However, this is caused by the compression, not by the media player, and the best media player in the world can't do a thing to help if the audio files it is playing back are heavily compressed.
Included Headphones (3.30)
The final step in the chain of music to your ears is the headphones, and the iPod Nano comes with the standard Apple earbuds. We do extensive test to see how good these are, and we were not particularly impressed with them. We found that they did a reasonable job of reproducing the range of frequencies, but that they added significant distortion to the music, particularly at low frequencies. And, while they could handle plenty of volume, we found that they did very little to block outside sounds; even small noises get through them like they were not there. One way to deal with this is to increase the volume, but your fellow travellers won't appreciate this if you do this on the bus: we found that a lot of sound escaped from the headphones, so the person sitting on the bus will know exactly what kind of music you like, and may even be able to sing along with you.
The bottom line is that the iPod Nano can produce much better sound than the included headphones are capable of reproducing, so a better pair of headphones would be a sound investment if audio quality is important to you. And a better pair of in-ear headphones will also do a better job of keeping your music private; the included Apple ear buds are as leaky as a rusty bucket.
|
