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Old July 14th, 2002, 02:06 AM   #1
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4-channel capture, weird clicks

I'm having a problem with 4-channel audio capture over Firewire, and I wonder if someone can help please?

I bought a shotgun mic (Azden SGM-2X) for my XL-1S, and am feeding it into Audio-2 Left on my MA-200. Putting the camera into 4-channel 12-bit mode has the desired effect, with my onboard stereo mic recording onto the first two audio channels, the SGM-2X onto the third, and nothing on the fourth, with the gain turned all the way down. The audio sounds perfect on playback through headphones plugged into the XL-1S analog output.

When I capture, using Scenalyzer, on my desktop PC, I get clicks about every 1/4 sec, getting louder as the audio gets louder. When I capture on my laptop, the problem is the same. The problem is only with channel 3 and channel 4 capture. Everything works fine on channels 1 and 2, regardless of whether they're 12-bit or 16-bit.

My PC is a generic home-built P4 1.8GHz, Intel 850MV motherboard, 512MB RDRAM, Sound Blaster Live and the generic TI OHCI Firewire card that comes with Pinnacle Studio. OS is WinXP Pro. My laptop is a ThinkPad A30P, also WinXP Pro.

I swapped the connections between the MA-200 and the XL-1S, so that the MA-200's channels 1 and 2 fed into the XL-1S's channels 3 and 4. The problem persisted, so it's not just faulty channels on the MA-200.

Any ideas? Given that I'm using two different capture platforms, it seems unlikely that it's related directly to my hardware. I'm using Scenalyzer Live on both platforms, so that's a common factor. I'm wondering if there's something wrong with my XL-1S, although audio played off the tape sounds perfect through headphones. I know that the mic is working fine, because it doesn't exhibit this problem when fed into channels 1 or 2. Thanks!
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Old July 14th, 2002, 08:11 AM   #2
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I'm not a PC guy, sorry. But not all software supports 4 channel capture of audio. Is there a preference or setting in the software to change for 4 channel or 12 bit audio? I've read posts here of people using Scenalyzer so hopefully one of them will chime in.

Jeff
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Old July 14th, 2002, 08:59 AM   #3
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Does the sound play OK via analog out?

Can you get clean 4-channel capture wiht other systems?

My guess is a problem in the capture process where in for some reason your capture softwasre is having a problme with the channel 3/4 digital audio stream.

A good place to explore may be the support forums for your capture system.
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Old July 14th, 2002, 10:23 AM   #4
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Some NLEs Have Problems with 4-track.

Discreet's newsgroups discussed a similar problem with Cinestream. The speculation was that 4 track is recorded at 12 bit resolution (32kHz) and if you mix 48 and 32 in the same track you can get annoying clicks from resampling by the NLE.

The consensus was to keep 32 KHz stuff separate from 48KHz. The rendered track, can be either 32 or 48KHz without any problems.

Nathan Gifford
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Old July 14th, 2002, 11:26 AM   #5
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Thanks for the replies.

To answer Don's questions: yes, the sound is perfect via analog out and no, I don't have any other way of getting 4-channel capture other than using Scenalyzer's "second channel" capture option. Sound Forge reports the audio as 16-bit 32KHz, so Scenalyzer or something else along the way is upsampling from 12 to 16 bits. But, that shouldn't cause annoying clicks. They certainly sound like resampling errors. The clicks appear even during audio preview during capture, so this isn't something that an NLE is introducing.

Maybe this is because I'm using a generic (Pinnacle) OHCI card? However, I get the same problem on my laptop, although that, too, contains a TI OHCI chipset. I'm thinking of getting a DVStorm, which may solve the problem....
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Old July 14th, 2002, 07:46 PM   #6
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Mabe take a look at the wave file to see what the clicks are. Probably a gap/break in the waveform. Have you tried to capture from a different playback machine?

An alternative worka round is to capture the first two tracks via the firewire, and to capture the other analog via your sound card, and then sync them in post.

Unusual perhaps that it takes it to 32k/16-bit.
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Old July 14th, 2002, 08:42 PM   #7
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Duh. You're right, Don. I stupidly forgot that I have a Sony camcorder to try capturing from. I'll give that a try. I emailed the author of Scenalyzer, and he's looking into it, too. He said that he'd let me know tomorrow if it's a bug; great service, no?
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Old July 14th, 2002, 09:47 PM   #8
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I tried my Sony TRV-10, and here are the results:

The tape recorded on the XL-1S has the same problem playing back on the TRV-10: the second stereo pair captures with the same loud clicks.

Recording a 4-channel tape on the TRV-10 has the same problem, except to a much lesser degree. The clicks are there, and very noticeable, but not as loud.

So, this kinda sorta eliminates the XL-1S as having a problem, although not completely, because it's much worse on the XL-1S.

The only common denominators between all the various combos I've tried are the tape (Sony Excellence, so I don't suspect it of foul play), TI OHCI capture chipsets, and Scenalyzer Live.

If anyone's interested, I have a 160kb .wav file with the offending clicks, which I can email to you for your comments. Thanks, as always!
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Old July 14th, 2002, 10:37 PM   #9
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I just came across the same problem. Recording with both the onboard mike plus house sound running into audio 2, I get clicks and pops when I capture using Scenalyzer. Playing out the analog ports audio on all channels is fine. Please keep us posted with what you find.
-Brad
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Old July 14th, 2002, 10:48 PM   #10
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Ah, the sweet, and totally irrational, relief that one gets when you discover that "they all do that" :-)

I'll certainly keep y'all informed.
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Old July 15th, 2002, 06:20 AM   #11
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OK. Email the file to me at:
dpalomaki@cox.net.

Would be interesting to try the tape with a different capture system.
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Old July 15th, 2002, 08:11 AM   #12
 
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Standard PCI sound cards for the PC, like the Soundblaster series, all have PCI bus latency issues. The Soundblaster is notoriously problematic around this latency issue. There is a patch for the latency issue available from www.viahardware.com, as well as an explanation of just what the latency issue is. Most noteably, it causes pops and clicks during playback and recording. If you're serious about your video and audio, I would highly recommend replacing these run of the mill sound cards with a professional sound card from Midiman, Tascam, or EchoAudio. You'll find the low latency and residual system noise is an order of magnitude better with any of these professional, digital sound cards.
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Old July 15th, 2002, 01:42 PM   #13
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I use an Azden wireless mic connected to an MA-100 which is connected to the left side of stereo 2. I am using a manual gain setting on that channel. I am also using Scenalyzer Live to capture the second channel and have not noticed any clicks. Is it possible that the signal was recorded to hot and it just isn't as noticable until the signal reaches the computer?
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Old July 15th, 2002, 03:11 PM   #14
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I agree with Bill's coments about the SoundBlaster, and a sound card upgrade is on my list. However, in the the case of DV capture and editing, the SoundBlaster is merely a preview device and never plays a role in the encoding, manipulation or decoding of the sound. Of course, it'd be nice to know that the preview is as close as possible to the original, and the SoundBlaster is at best a "draft preview" solution only.

It's possible that the captured sound is perfectly ok and that the SoundBlaster is messing it up. However, as the problem only occurs on channel 3/4 capture, and almost identical sound on channel 1/2 sounds ok, I don't think that it's the SoundBlaster.

To Edward's point, I thought that this might be the case, but the problem exists in captures that are recorded with significantly lower audio gain, too. I'm interested in what your capture solution is, though. Is it generic TI/OHCI, or something meatier?
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Old July 15th, 2002, 08:06 PM   #15
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See the sound card reviews at: pcavtech.com. Some good information there as regards sound quality of many common sound cards in the low to moderate price range.
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