How does the audio compare?
All of the cameras in this test possess varying levels of sound recording capabilities, from relying entirely on the built-in option to having the capability to accept an external mic. As sound is just as important as audio when shooting movies, it's worth comparing the end quality.
The EOS 5D Mark II produced some impressive, extremely clear audio with no audible compression or favouring of the operator's voice over other environmental noise. Its sibling, the EOS 500D, is similar in terms of producing a reasonably balanced end product, although the higher frequency sound is too loud on playback. At the other end of the scale, both Nikons showed a high amount of compression in the audio quality as with the video, with the end result being tinny and unable to cope with alterations in volume or pitch without distortion. The D5000 actually produced a marginally better balanced result, but with a lack of external mic support there were no options to make any improvements to what is recorded on board.
Panasonic's GH1 sound was slightly muffled and favoured the lower frequencies, and has a rather annoying bespoke audio input which requires an adaptor to connect a standard mic. Panasonic's own brand directional mic is excellent though, making it less of an issue. The Pentax K-7 came top of the class though, not only producing excellent built-in audio but also having an audio meter and the ability to plug in a mic without any further attachments required.
The audio quality moves in peaks and troughs, as shown here in an example of the EOS 5D Mk II's wave form, increasing for higher frequency sounds and dropping for lower frequencies.