Test Bench #3
iPod Touch
Audio Measurements
Test Bench #2

Selecting CD
Storage Format
Test Bench #1

Centrace MicPort;
MXL Mic Mate
Foster's Test Bench #3:
iPod Touch Audio Measurements

by Alvin Foster with Stephen Owades

The iPod Touch is a portable media player, personal digital assistant, and Wi-Fi mobile platform designed and marketed by Apple Inc. The product was launched in September, 2007. The iPod Touch has a multi-touch screen and a graphical user interface. Originally it was available with 8, 16, or 32 GB of flash memory; the current line includes models with 8, 32, and 64 GB.

The iPod with supplied earbuds

I purchased the iPod Touch model MB528LL, Version 2.2.1, about six months ago for $240.00 ( ). It has a capacity of 8 GB and a tiny internal piezo-electric speaker. The iPod's sound is essentially unintelligible at a distance of more than 12 inches from the device. The original iPod did not include a speaker.

I have no interest in using the iPod's audio output to listen to music although it boasts an easily accessible plug for headphone listening. I use it almost exclusively as a remote control. As such, it selects the album to play — no audio signal from the iPod enters my listening chain. However, because millions of people use iPods as a source of music and video entertainment, I am curious about its frequency response, distortion, output impedance, channel separation, maximum output, square wave reproduction, and S/N ratio.

iPod Features

To list all the features of the Apple iPod Touch would require too much space. Most of the features will never be used by me and possibly most buyers. The Touch does not have cell phone capability. It does have e-mail ability. These features permit me to leave my laptop at home for short, out-of-town trips accompanied only by the iPod Touch.

The iPod remotely controls my hard-drive, computer-based CD/DVD player/recorder. To date, I have loaded about 30 albums onto my computer's HD in the Apple lossless format. The Touch can operate the iTunes application on my computer from almost anywhere in my house by means of Wi-Fi. The "Remote" application, a free download from the iTunes store, controls album selection, volume control, rapid advance within a selected track, etc.

CD-based music is imported into the iTunes library by inserting an audio CD into your computer's disc drive and clicking on "Import CD." If you have an Internet connection, iTunes will (usually) automatically retrieve the song's title, artist, and other information. The tracks can also be loaded onto the iPod Touch if you want.

The iPod's color screen displays a list of the tracks available on the computer's iTunes library; if the music has also been loaded onto the iPod Touch, a display of the album cover art is also offered. The track listing, name of artist, and much more are available with a few easily memorized steps. The iPod permits music selection also by searching for a song title, artist, etc. It is a nice addition to my computer-based playback system. I am using iTunes now in place of Microsoft's Media Center, because the latter was problematic and didn't include a few features I wanted. The MS Remote Control, for example, cannot fast-forward within a CD track, and it employs infrared to communicate with the MS audio software. Infrared roughly requires line-of-sight for consistent connectivity. The Media Center only displays album artwork on the computer's monitor and not on the companion remote. The information on the computer's monitor, however, was consistently more useable and the print size larger than what is displayed on the monitor with iTunes.

To control the iTunes software audio level, there is a volume up/down button and the touch icons are brightly displayed on the smallish screen. The touch icons provide the primary access to iPod's many applications and iTunes.

The photo below illustrates the CD/DVD album display capability of the portable media player with Apple's CoverFlow (available only for media that has been loaded onto the iPod). One selects an album by touching the desired album cover. The selected CD is exhibited and the play options for the album are displayed.

It takes time to learn where and how to touch only one button at a time. Even after months of use, it still often takes me several tries to select the desired feature or application. One gets the sense that the iPod was designed for people with extremely small fingers. The built-in RF feature is great but it has problems. It sends signals inconsistently to the computer. It often requires multiple button pushes and ‘random' aiming to obtain some sort of consistent control. Often when the CD/DVD player does not respond, I reorient the iPod so that the RF signal path is established. (Remember, the iPod isn't communicating directly with the computer, but rather with the Wi-Fi base station, which takes some getting used to!)

Connectivity, Size, and Battery

I have found the iPod's Wi-Fi unpredictable and inferior for connecting to the web when compared to the built-in Wi-Fi connectivity of my Toshiba Qosmio Laptop Computer. On several occasions, I have placed the iPod and the Toshiba side by side. The laptop easily links to the ISP or web site while the Touch remains unconnected to the hub. A trip back to the Apple store declared my Touch was working fine; however, the unpredictable ISP connectivity continues. Often when out of town, it sometimes fails to connect to the hotel's router even though others using laptop computers are surfing the web and having fun.

The iPod Touch weighs in at 4.05 ounces. The size in inches: 4.3 high x 2.4 wide x 0.33 deep. The high quality 3.5 inch (diagonal) widescreen, multi-touch display has a 480-by-320 pixel resolution at 163 pixels per inch.

 The iPod showing dimensions  

There is an interesting UK review here:

The unit has a built-in rechargeable lithium ion battery. Apple claims up to 36 hours of music playback time when fully charged. I could get no more than two hours of continuous use. The battery is not user replaceable, and Apple charges $79 to swap your iPod for a new (or refurbished) one. If your model is not in stock, a comparable iPod will be sent.

The audio output level of the iTunes software is controlled by a volume up/down button on its side and an icon on the glass display. All touch icons are brightly displayed on the smallish screen. These images provide the primary access to the iPod's many applications and iTunes.

The iPod Touch has a 3.5-mm stereo headphone jack and a unique Apple "Dock Connector." A cable plugged into the Dock Connector terminates in a USB plug for the computer. The computer's USB port provides power for the iPod, updates, and the ability to ‘Sync' with the iPod (to transfer photos, songs, videos, etc., from the computer to the iPod Touch).

Memory and Costs

The iPod Touch memory size is available now in 8, 32 and 64GB. The most expensive unit with the largest memory sells for $399.00 from Apple. For my use the smallest memory size works. It holds about 23 of the thirty albums on my computer. It will not display all the albums if the playlist CDs exceed the internal memory capacity. To get around the memory limitation, I use a custom Playlist containing only the songs I want to hear. With Remote, I can also access all the material on the computer's iTunes library, albeit without the fancy CoverFlow display on the iPod Touch. Furthermore, I could not justify the huge price difference for additional memory which costs Apple incrementally so little. Although the original iPod Touch models were the same except for memory capacity, the two larger models in the latest generation have faster processors and a few additional features.

Audio Tests

Apple claims a 20–20,000 Hz response for the iPod Touch. No distortion or level-dependent information is shown in the literature supplied with the iPod. To perform the following tests, I imported the CBS Records CD-1 into iTunes in Apple Lossless format. After connecting the iPod, the Syncing process placed the CD onto the iPod. The iPod's headphone jack was then connected to my computer-based audio analysis software, SpectraPlus (a PHS product that retails for $295–$1295, depending on selected options). SpectraPlus provided a complete spectral analysis of the iPod's audio signal.

To my surprise, the iPod Touch did very well in the tests. All tests were run on a fully-charged battery, and the iPod's volume control was set to maximum. The audio signal from the iPod fed my desktop computer's E-mu 1616M PCI outboard converter. A 30 kHz low-pass filter was used in the tests.

Maximum Output and Distortion: The maximum output and distortion with no load at 1 kHz was 1.04 dBV rms and 0.009% THD. The numbers did not change for loads between 300 to 600 ohms. The unit is easily able to cope with most headphone impedances because the output impedance approaches the ideal, 0.9 ohms. The S/N ratio was –79.5 dB. At a more likely 0.5 dBV rms output level, the distortion was 0.014% and the S/N was –76 dB. The 2nd through 5th harmonic distortion components never exceeded –75 dB. The IMD was 0.008% using the IM standard 60 and 7,000 Hz tones.

Frequency Response at 0.75 dVB rms output, both channels into 300 ohms: 17–16,000 Hz was flat. Between 18–20 kHz the unit was down 0.1 dB, excellent. The highest THD occurred at 12.5 kHz, –55.5 dB, good. Channel separation was typically –50 dB, OK. The output imbalance between channels never exceeded 0.7 dB at 18 kHz, good.

Square Wave Performance: A small ripple was visible, typical for A/D converters. The ringing occurred at the leading edge of the 1 kHz square wave, very good.


With iTunes and the iPod Touch, you can import and manage your CD music collection. Place an audio CD into your computer's disc drive and click Import CD/DVD. In my system the iPod's audio output is unused.

The Apple iTunes Touch presents a nearly distortion-free signal to almost any headphone. The frequency response is smooth and good enough to drive a decent quality hi-fi system, if desired. I only tested audio quality with Apple lossless compression, so I can't say how lossy compression (AIFF or MP3) would affect these results.

The tiny buttons on the iPod Touch take time to get used to. To date, I'm finding it almost impossible to select a button without touching an adjacent key. The short-lived internal battery is only good for about two hours of manipulating iTunes, because keeping Wi-Fi active uses a lot of power. The iPod must be connected to the computer's USB port, or an external AC adaptor, for recharging. The unit will operate with the connection cable plugged in.

The home screen has a list of icons for the available applications that are too numerous to list and for me go mainly unused. Lest anyone forget, it plays music too. The touch includes Apple's Cover Flow, a handy way of browsing albums by cover. Currently, the iPod Touch is serving as my iTunes remote control for my media center until something more reliable and with larger print comes along.

— Alvin Foster  October 6, 2009


updated 10/9/09


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updated 10/9/09