EDIT May 25th 2010
I have so far confirmed this “bug” exists in CS4 and CS5, description and two possible solutions follow below

Recently I’ve been testing a JVC GY-HM100 HD video camera (or GY-HM100E to be precise, since it’s a European variant) and I’ve uncovered an issue with audio imported in Adobe Premiere CS4 that appears to be badly documented. Note this is not a review of the camera. I’ll have to do much more work with it to pass any judgement, so for now I direct you elsewhere for opinions on how the camera behaves.

I first noticed the sound issue when I imported MP4 files into Premiere CS4 (GY-HM100 can also record MOV files which I have not tested). The problem is that on some parts of a clip the waveform goes crazy and there’s nothing but very loud noise (maxed out) on both or just one of the channels for a few seconds but then it goes back to normal. You can imagine my shock when I first played back a very silent clip of a pre dawn nature shoot with speakers near maximum only to receive a proper wake up “hum”.

same clip, two very different waveforms (original left, converted version on the right)

The files are otherwise fine when played through other software such as VLC player. Other people report the same thing is happening in Soundbooth CS4. Yes, I tried it out and the same thing is there as well but I never used it before so for me it hasn’t been an issue. Why or how this is triggered is still a mystery to me. It seems to be independent of mode/resolution (I was shooting in 1080p and 720p), type of sound recording (external or internal mic) or (based on forum discussion) operating system. I’m not sure how exactly but it would appear to be a codec problem in Adobe CS4 rather than anything being wrong with the camera.

The DVinfo forum thread does provide a temporary bypass though. And it is to be found through a conversion tool MP4toMPG by MIK Digital that converts audio (mp2 @ 320kbps) and copies the video 1:1 into an MPG2 container file. In short, it does the job. The app is written in German, however it is very simple to use and does everything in 3 steps:

1. select source folder
2. select target folder
3. execute

Obviously converting files is not a long-term solution and I’ll keep searching for an answer. But for now this hack/bypass will have to do so we can keep shooting and editing the footage.

Featured comment (segment) by Fredrik Lindau

I have found that if you copie the whole map-structure from the memmorycard to your harddrive the clip works fine. But if you only copie the MP4-file you get this sound issue.

The above mentioned solution has now been confirmed. Simply copy the entire directory structure (not just the clips or clip folders) from the card and audio will play just fine in Premiere CS4 and CS5. It’s a bit of a mess to find specific clips but ultimately it avoids transcoding so there you go.