Let me start by saying I am by no means an expert at data comparison studies or methods. Nonetheless, I decided to compare the new iPod Touch 5G with the previous iPod Nano 6G. The iPod Nano 6G contains the same Cirrus audio DAC (digital to analog converter) as the iPod classic that I've used for over 5 years, which is also found in a few other iPod models. I'm not sure which DAC the new Touch uses, but I've put it up agains the Nano 6G for comparison.
This test focuses on the headphone output jack, as the digital connector should theoretically be identical on each device, because it bypasses the iPod amplifier and sends just the audio data directly to your external equipment. Let me describe the testing method and equipment used.
For recording the audio files, I have used a monster 3.5mm to 1/4" balanced stereo audio cable. This connects the iPod headphone output to the 1/4" instrument inputs of my Apogee Duet audio interface. Both iPods were recorded using the maximum iPod volume level with no audio equalization or settings applied. Anything that would alter the original audio quality on the iPod is deactivated and the audio files transferred to the devices were in apple lossless format. This is as pure as the iPod audio gets.
I chose the song "Freedom at Midnight" by David Benoit, because this is one the best recordings I've ever heard. It contains clarity, depth, bass and separation that are simply of the highest quality. I also di the same test with "Never Let Her Go" by David Gates, but I will only include the David Benoit results, as they are both comparable.
I used Logic Pro to record the audio at the matching 16-bit 44khz audio quality that the original files are encoded in. After recording the audio files, I used a combination of Soundtrack Pro and Audacity to analyze the audio data and make comparisons. The following are my results.
First, the iPod Touch 5G seems to have an ever so slightly louder output level. Overall, the sound quality of the iPods is practically identical. First lets look at the waveform of each file (iPod Nano 6G on top half, iPod Touch 5G on bottom half):
As you can see they look pretty much the same. According to Audacity, the RMS (mean volume) is identical:
The frequency curve is also identical. If you look carefully though, you can see the iPod Touch 5G in the bottom image has a lightly slightly greater output. This can be seen by the entire graph being a little higher on the y-axis which is the volume (db):
iPod Nano 6G:
iPod Touch 5G:
Next we'll look at some spectrograph, which shows the amount of energy of specific frequencies over time. This was configured for a maximum dynamic range of 100db to include the full 96db of CD dynamic range and 22khz maximum frequency to allow the full range of frequencies in the 44khz CD sample rate (see audacity manual).
The first view is the full length of the song (iPod Nano 6G on top half, iPod Touch 5G on bottom half):
An even closer view still (iPod Nano 6G on top half, iPod Touch 5G on bottom half):
This view reveals something interesting; the two iPod play music at a slightly different speed. This is a very close zoom level and a very small difference at only 1/10th of a second by the end of the song, but it is there. Probably too small to amount to anything in the real world. 1/10th of a second over a few minutes is probably not an audible difference at all at only .4%. Interesting nonetheless...
Lastly the spectrograph analyses from Soundtrack Pro:
iPod Nano 6G:
iPod Touch 5G:
iPod Nano 6G:
iPod Touch 5G:
At first they might seem identical, as in the all of the above screenshots, however there are subtle differences. Take a very close look at the data from both programs:
Audacity (iPod Nano 6G on top half, iPod Touch 5G on bottom half):
Soundtrack Pro (iPod Nano 6G on top half, iPod Touch 5G on bottom half):
Although very small, there are some differences in the trails of data. Look at the slight differences in the faint data at the top of the Audacity views. Also note the difference in darkness of the straight horizontal line about a third up from each half of the Audacity view. On the Soundtrack Pro view note the right side edge of some of the green spectrum data. There are slightly different shapes and forms. These are very close looks at the data, so in reality, I doubt any of this is audible.
If I had to guess, I would theorize that some of the difference seen are coming from the inherent noise in the analog systems and cables. Every analog system has some small noise, and perhaps this noise is being seen at these extremely close views? If that is the case, the noise would be random, causing the slight differences here and there. Or perhaps there is some other interference? It is even possible there is simply a slight difference in audio processing or amplification. Perhaps the slight difference in output gain is the cause? Honestly, I have no idea.
However, in true listening tests and the relative comparison of data, I believe these difference are most likely not having any effect on the audible quality of the devices. I have compared 256aac and 320aac files to lossless audio files, and the differences are greater than you see here.
In conclusion, I would call the audio quality of the iPod touch to be in line with the previous iPod Nano 6G, iPod Classic 160GB, iPod Touch 3G, iPod Nano 2G and possibly others. These are the only iPods I have to compare, and while I haven't done extensive data analyses of all of them, I have done very excruciating listening tests, and they all appear to be the same basic quality.
I don't know which audio DAC is in the new iPod touch, or the old iPods mentioned, but after some research I think the implementation of the DAC in the entire audio system of the iPod is more important the the DAC itself. That is simply based on second hand information, but the listening tests appear to verify this claim if in fact any of my iPods have different DACs.
If you have the new iPod touch, I'd love to hear your opinion on the audio quality. Please leave a comment below. But most of all, go listen to your music and enjoy it. Isn't that the point of all of this? :-)