Audio noise only on HI-FI VCR after export at

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Old December 29th, 2001, 12:46 AM   #1
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Audio noise only on HI-FI VCR after export

I just finished filming an outdoor project using my XL-1 and used iMovie to edit. I used the 16-bit audio mode and used the supplied mic attached to a boom pole to get close to my subjects. I've had some of the same audio "pop" problems on export like many others I've read about. But it only occurs occasionally - so I can eventually get a "clean" export back to DV tape. I got a good export to DV with no audio problems. Then I dubbed from my XL-1 to VHS and it came out fine -- UNTIL I played it back on a Hi-Fi stereo VCR. The playback had pops and buzzes all over the place. So I went into the VCR menu and switched sound output to MONO and the pops were gone. So it seems that the audio "glitches" were only on one channel--??? But when I listen to the DV tape with headphones while it plays in the camera, it sounds fine with no pops.

I'm very new to all video/audio stuff -- so I barely understand any of it and am learning as I go. Can someone explain the process of sound export from the computer to the XL-1?? Does the camera record all the sound on one channel or both when you export from the computer?? Does anyone have any idea what my problem might be??

For now -- I just set the VCR input to record MONO sound and so my VHS tape is fine. But I'd like to know if there's a fix so I won't get the audio pops when I play back in STEREO on a VCR. I hope this is not too confusing and I also know it combines an XL-1 question with an iMovie question -- so I hope this is the appropriate forum.
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Old August 15th, 2002, 03:49 PM   #2
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This is a very old thread but maybye somebody is still interested....

I had similar experience in the past. As you know - VCR has rotating video heads to record picture. Early (MONO) VCR standard was designed to record sound using separate audio head located close to the edge of the tape, just like in the traditional tape recorder. Stereo VCR recording is however completely different story. Stereo sound is added to composite video frequency recorded with rotating heads. Due to some technical details I don't want to get into - this gives much better quality (HiFi) than 'conventional' audio head. If you however only record stereo sound on the tape - older mono VCR's will not find their MONO sound expected to be on the edge of the tape. That is why - only for backward, mono compatibility - stereo VCR's still have that additional mono head and additional - mono - sound channel. I found however the quality of that channel (recording) very poor, at least in my SONY stereo VCR. I guess one of the advantages of PRO duplication VCR units is good MONO compatibility with old VCR's. But so few people need it this days that makers of new consumer equipment couldn't care less.... The conclusion is however - be careful and try not to play back stereo home recorded tapes on mono VCR's.

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Old August 15th, 2002, 08:09 PM   #3
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Sounds like somethig is strange in the iMovie setup. How did you make the VHS tape - what VCR and what settings? How was it connected to the NLE system.

VHS stereo HiFi sound is a FM signal that is recorded along with the video information, but at two frequencies (for left and right channels) sandwitched between the luma and chroma signals. It should be very clean and crisp, about like FM broadcast quality.

If you can, listen to the audio output from your NLE that you are feeding to the recorder. If it is clean, then your record VCR may have a problem. Note, if you are connected to the viewing system via an RF (channel 3/4) connection, you may have something strange going on in the VCR playback-to-RF system, possibly clipping/saturation in the audio section.
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Old August 16th, 2002, 05:17 AM   #4
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The Hi-FI tracks also need to be adjusted with the tracking control. I've had HI-FI VCR's that play video fine (didn't need to adjust the tracking). But the HI-FI audio would go in and out and pop etc. Adjusting the tracking would bring in the audio, but sometimes the video would get fuzzy. Get the picture right and the audio goes out. Switch to Linear (mono on some VCRs) and the audio was fine. The solution was to get a tape path alignment.

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Old September 22nd, 2002, 02:30 AM   #5
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I don't know if this is relevant, but my friend has two decks, both cheap, one a mono player only. He records his shows then plays them on the player-only to re-record w/ out the commercials and the sound goes out of synch. Sounds like a similar concept of mixing of the audio between stereo and non.
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Old September 24th, 2002, 06:56 PM   #6
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Also, I think that there could always be some trouble with the 48k clock re: audio. I've wondered if there are some issues with a track that for instance is captured at 48.0005k (as I've seen) and then playing on a true 48k system.

I've found that if I ever use a clip in FCP, where there's a reported TC break on capture, I get problems that don't seem to exist until you really look/listen to it.

If there is any trouble with the audio not being at 48k, I suggest buying, QT PRO for $30 from Apple. It allows you to make a copy with whatever settings you like. I'm not sure if iMovie is a QT based system. Start QT and try to open an iMovie clip and read the data from an "info" type menu where it describes the frame rate, length, etc. If it's off, but QT pro.
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