There are two main things that contribute to the sound quality of an iPod. One is the audio chip that is used. This is the chip that converts the digital data into the actual sound. It is called a Digital to Analog converter or DAC. The other is the combination of components along the audio path from the audio chip to the headphone jack – a mixture of op-amps, capacitors, resistors and inductors.
The iPods I like the best seem to be those that use the Audio chips from the Scottish company Wolfson. When I detected this difference I didn’t know what a Wolfson chip was, but I could definitely hear a difference and so I did some research. It turns out that my two favourite iPods that i owned at the time of first discovering this – the Nano and my 4th Gen iPod – both had a Wolfson chip in them. The iPhone 3Gs did not.
Of all the iPods that use the Wolfson chips, the 5th generation iPods appear to be the best, followed by the 4th Generation iPods. Check out these comments by Vinne from Red Wine Audio. (That is an archived version, the updated website is here but it has less information.)
The sound quality of course depends on more than just the chip that is used, so it’s not just about which chip is in the iPod. My Shuffle first gen and also the second gen model A1204 (non-wolfson) sounds great, as does the iPhone 4S. [I have since been informed that the 1st Gen Shuffle uses a ‘SigmaTel’ audio chip that has outstanding audio quality. I have not confirmed this.]
Red Wine Audio offer mods of the 4th gen and 5th gen iPods where they will replace the output section of the iPod with high quality Black Gate NX-Hi-Q capacitors. According to onheadphones.com the output audio quality rivals that of $1500 CD-players, with improved bass response and clear high end. (There is an excellent forum here on how to do the mod yourself!)
If you want the best possible audio quality, try and get hold of one of the fifth generation iPods – model number A1136. This includes the iPod 5G, iPod U2 5G, iPod 5th Gen enhanced and iPod 5th Gen with video.
The 5.5th Gen ‘Enhanced’ is hard to spot because it has exactly the same model number as the 5th Gen iPod. (A1136). The only way to tell the ‘Enhanced’ apart is that it has a ‘Search’ option in the software. (See here for more details).
Here is a great article by Marc Heijligers examining the iPod Classic against the iPod 5th Generation. [Thanks to Clive who has found this archived copy of this article after the original one disappeared.] The article was also quoted here. Marc’s homepage is here. I have made a pdf copy of it here in case it goes missing again. Here is a quote from the article:
“I noticed that the 6G sounds precise, crisp, but lacks 3D image and has an electronic haze to the sound. At first, this might sound like an improvement (crisp, detailed), but when listening more carefully and for longer times, it becomes fatiguing after a while. The 5G sounds less precise, but its timbre contains more harmonic information and sounds less electronic. For me, the 5G is closer to how I experience acoustic music in real life, and for me is the better sounding device overall.”
He then goes on to do some measurements to back up his findings.
This was his conclusion:
“From these measurements it is obvious that the new audio circuit of the iPod Classic is badly engineered compared to the iPod Video:
– Treble has a slight uplift.
– The group delay is not linear over the frequency range.
– There is significant intermodulation distortion with a 22.1kHz component.
The measurements show a correlation with the things I hear, but from a pure scientific perspective the cause-consequence is not determined by these measurements. The measurements show some flawed behavior of the audio circuitry, which so-far is the only thing that can be concluded without any doubt.
Overall, the 6G overall sound performance is disappointing to me, especially considering the well-sounding 5G. Does it mean you shouldn’t buy an iPod 6G? The way the change of sound quality is perceived will vary per individual. Therefore I recommend you to judge the 6G individually, and don’t let ourself be guided by my opinion, or some measurement graphs.”
This test shows iPhone 4S has better specs the iPod Classic 6G and the iPad 2, but I can’t’ find any direct comparison between the iPhone 4S and the 5.5G iPod.
iPod Touch 1G (WM8758BG)
iPod mini (Wolfson 8731?)
In summary, all the early iPods up to 5G Classic used Wolfson chips.
ipod ‘Classic’ 1G , 2G & 3G (CS42L55) (These are also known as 6th 7th and 8th gen iPod)
iPod Touch 2G (possibly CS42L58)
iPod Shuffle 4th Gen (CLI1544C0)
Cambridge Audio and Harman Kardon use Wolfson DAC chips in their CD players. Pioneer, NAD and Onkyo use wolfson in some of their CD players. Marantz use the Cirrus Range. So it’s not just about the chip – the other audio components will make a difference too.
Here’s a rave review of the 3rd generation iPod (has a wolfson chip) from Stereophile magazine from 2003.
This article was first written in 2010, and Apple keeps improving the audio quality with every iPod released, but I think these results still stand. Check out this thread for some other raves about the 5.5G iPod compared to the later models. There will always be new models coming out – keep an eye on head-fi forums and so on for reviews.
2011:Recently the 7th Generation Classic has been released and some people prefer the 7 to the 5.5. There’s a great debate about the 5.5G vs 7G here and here. It seems the 7G is more accurate and precise, however the 5.5 feels warmer.
2011: It’s rumoured that with the iPhone 5 Apple will be returning to the Wolfson chips, but we’ll see! (Note: The iPhone 5 was been released and they didn’t, same for iPhone 6).
2015: Apple have released iPhone 6, no wolfson but you can still use the lightning to 30 pin dock adapter which has a wolfs chip in it.
If you are after good audio in an iPod the older ones are the best. (especially the 4th and 5.5th Gen classic era)
iPod 5.5G Enhanced (wolfson WM8758)
iPod 5G (wolfson WM8758)
iPod 4G (wolfson WM8975)
iPod nano 1G and 2G (wolfson 8975).
(iPod Classic 7G might fit in here, see discussion here.)
SOME CORRECTIONS I HAVE MADE TO THE ABOVE ARTICLE:
“The iPod Nano 2G uses the Wolfson DAC. It is the iPod Nano 3G to 6G that uses a different DAC.” by ArtMuzz here: http://www.head-fi.org/t/580987/has-ipod-changed-their-sound-chips-cards-from-generation-to-generation
“In the case of the 1st gen iPod Shuffle, it was a SigmaTel audio chip.” also from here: http://www.head-fi.org/t/580987/has-ipod-changed-their-sound-chips-cards-from-generation-to-generation