Does your iPod sound nasty when you turn it up loud?

Not that I listen to my iPod loud, or usually at all for that matter. (You shouldn't listen to yours loud either: it will damage your hearing, which you will never get back once lost, and besides, extra volume is almost always an unsatisfactory compensation for a lack of fidelity somewhere in your system that you should seek, locate and correct. But I digress...) My iPod is filled with uncompressed music that I use as a (relatively) high-quality source when prototyping and building amplifiers.

Today I needed to feed a preamp with a 1kHz sine wave. I have an audio CD full of sine waves (and other torture devices) so rather than build a cheesy little signal generator out of an op-amp and a light bulb I thought I'd be ever-so-21st-century about it and upload the CD to my iPod to turn it into a signal generator on steroids. And lo...

This is what a 1kHz sine wave looks like, playing on my iPod with its volume control set at one notch less than maximum:

1kHz sine wave

Pretty, isn't it?

This sine wave is recorded at '0 dBFS' (which is geek speak for saying that it is at, but not beyond, the maximum amplitude that digital audio should correctly reproduce). When fed with a 0 dBFS sine wave a well-behaved system produces exactly the waveform above, and will do so regardless of where you set the volume control (above zero). So far so good.

Here's the same 1kHz sine wave played with the iPod volume increased (by one notch) to maximum:

1kHz sine wave

The built-in amplifier in the iPod can't cope: the waveform is horribly clipped, with the peaks and troughs severely flattened. This might not have been disastrous fifteen years ago (when there was still some dynamic range left in many recordings) but these days, with the loudness wars keeping most recordings at 0 dBFS as much as humanly possible, if you listen to your iPod turned all the way up then this is going to cause noticeable distortion (of the nastiest kind) on a lot of material.

When I did listen to my iPod a lot I almost always used an external headphone amplifier (to take the strain off the built-in amplifier with low-impedance headphones, or to get a reasonable level with high-impedance ones). The headphone amp had a volume control of its own that I used while leaving the iPod's volume alone. I never liked the sound with the iPod turned up full and now I know why: Apple designed the iPod's volume control to go all the way to '11', even though they probably knew that '10' was the limit.

(I get the same result regardless of load and regardless of power source, battery or charger. The so-called 'EQ' setting is off. The iPod in question is a 4G.)