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Old May 11th, 2008, 06:37 AM   #1
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Padding line down to mic level

I'm shooting races at a local short track and they provide the announcer feed through an XLR connection at line level. I want to also capture live sound using a shotgun mic. This creates a problem with the XH A1 as you cannot set one input to line level and the other to mic level.

My initial thought was to get a pad to put on the line input to drop it to a level that will be happy with a mic level input. However that's not working. While the the -40 pad drops it down to a compatible level, the audio is wicked distorted. If I remove the pad and switch the cam's input back to line, the feed sounds fine.

So I'm stuck. What am I doing wrong? If I can't lower the line level, how can I raise the mic level without spending a zillion dollars on a field audio mixer? All thoughts and options are appreciated. I've gotta come up with something soon because they're racing again next Saturday night.
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Old May 11th, 2008, 06:56 AM   #2
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Sounds like the problem is at the sending end. A pad doesn't distort anything -- it's a passive device that functions as a voltage divider. All it does is uniformly drop the voltage by a fixed percentage. It may also be that you need a -50 db pad, instead of -40.

They may have levels cranked up too high on the house board, causing clipping. Check to see if there's an independent level control for the line out you're using, and have them pot it down. The other possibility is that your pad is defective, which strikes me as unlikely. There isn't too much to go wrong in a pad, just three resistors.

Martin
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Old May 11th, 2008, 07:21 AM   #3
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Martin... thanks for the comments. I don't have access to the feed source, but their guy said he'd check how things were set and drop the level if he could, but I didn't notice any difference. I don't actually think he could make that change.

I too thought that the house board was over cranked but discounted that as the feed at line level (without the pad) is clean.

I'm pretty sure the pad's OK since I have two of them (switchable levels) and both reacted the same way. Thinking that -40 wasn't enough, I put them both in line and set them for a net of -60 (if -40 on the first one and -20 on the second add up to -60) and the net effect was the same. Could they both be bad? I just got both of them last week.

Still in trouble.
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Old May 11th, 2008, 08:21 AM   #4
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Still in trouble.
Sounds like you don't have a mixer. A Sound Devices 302 should work. Independent inputs.

Regards,

Ty Ford
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Old May 11th, 2008, 08:46 AM   #5
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Ty... I'm sure it would but it's a US$1,300 solution. Too dear. There's absolutely no ROI for this gig that could make that work.
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Old May 11th, 2008, 09:13 AM   #6
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you cannot pad an audio signal to adapt different input type.
while padding can decrease the audio level, it is not adapting impedance.
line and mic have totally different input level AND impedance.
typical effect of unmatched impedance is this saturated effect you got despite level looks good.
use some "problem solver" that have a transformer inside to convert signal impedance.
eventually use a good DI box providing several socket format as input and output, ground isolation, switch to pad -10/-20/-40 dB level and of course a transformer. such box ar cheap and can save your day in many occasion.

this one is on the very cheap side (passive)
http://www.artproaudio.com/products....cat=13&type=90
this one is specially for video (exactly what you are looking for in that case and cost 50$)
http://www.artproaudio.com/products....&cat=13&id=131
but you can find better one (active) .

Last edited by Giroud Francois; May 11th, 2008 at 10:59 AM.
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Old May 11th, 2008, 09:50 AM   #7
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Giroud... aha! Signal impedance. That's the part I was missing and it explains the garbage sound.

I checked out the link and it looks like it would do the trick except for thing. It takes a phono input which makes sense for its intended guitar application. I can live that.

I'll look around for other devices to see if I can get one with an XLR input, but if not I'll check with the local dealers.

Merci, mon ami.
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Old May 11th, 2008, 09:52 AM   #8
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Ty... I'm sure it would but it's a US$1,300 solution. Too dear. There's absolutely no ROI for this gig that could make that work.
just lookin' ahead. That's how I decide if it's a good ROI. If you try to get it all back from one gig, that usually doesn't work. If you do paid-for work, having a good mixer is a very useful tool, although I realize there may be a different approach to economics between MD and NH. :)

I use a SD 442. Last time I got a "Line level" feed from a mixer, it wasn't line level at all. It was sort of between mic and line. Rather than try to deal with the guy at the board who was very, very busy, I just took the feed and went with it, adjusting to suit with my mixer. We got what we needed.

Some ask why spend the money on a 442. The list is too numerous to fully post, but within the last week I had two situations.

1. I had to feed stereo to a camera, one track to an external recorder and one track to a Comtek transmiter. No sweat for the 442. Three sets of stereo outputs plus individual solo outputs for each input.

2. I had to feed two CD recorders simultaneously. One was a pro level XLR unit. The other had consumer line level RCA inputs. Consumer line level is -10, not 0 or +4. No problem, the 442 outputs mic, -10 or line level at the flip of a switch. You can even independently vary the L and R outputs of a stereo pair, one mic the other line or -10.

BTW, feeding pro line level to a consumer line level device can sound OK when you are sending tone at -20. HOWEVER....when real levels are attempted, the -10 input will clip if fed by a 0 dB pro line level source.

Good audio is not trivial.

Regards,

Ty Ford
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Old May 11th, 2008, 11:01 AM   #9
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sorry my 2nd link was wrong (corrected now). the box has XLR output and RCA/Jack input.
unfortunately it is only one channel , but it would work for you.
http://www.artproaudio.com/products....&cat=13&id=131
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Old May 11th, 2008, 11:25 AM   #10
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Giroud... aha! Signal impedance. That's the part I was missing and it explains the garbage sound.

I checked out the link and it looks like it would do the trick except for thing. It takes a phono input which makes sense for its intended guitar application. I can live that.

I'll look around for other devices to see if I can get one with an XLR input, but if not I'll check with the local dealers.

Merci, mon ami.
Take a look at this page on the Whirlwind site, especially their Direct-2 and Direct-2JT down near the bottom of the page if you need stereo. Still 1/4 inputs instead of XLR but adapters are readily available and cheap - Whirlwind makes good quality units. http://www.whirlwindusa.com/dirbox.html Also http://www.whirlwindusa.com/tech02.html for technical background info
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Old May 11th, 2008, 01:12 PM   #11
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Take a look at this page on the Whirlwind site, especially their Direct-2 and Direct-2JT down near the bottom of the page if you need stereo. Still 1/4 inputs instead of XLR but adapters are readily available and cheap - Whirlwind makes good quality units. http://www.whirlwindusa.com/dirbox.html Also http://www.whirlwindusa.com/tech02.html for technical background info
The box that sums the thru input with the regular input is very helpful. (I just use a y connector for the things I use a box for).

The DI box can be useful even if you have a mixer. I use one to take the unbalanced line out from a CD player/Amp and run it 100 feet to the camera. The box gives me a balanced signal that gets rid of my problems of interference with extension cords, etc. I also use the box for the output of a keyboard, changing it to a balanced, low impedance signal.

I don't know the details, but I believe the Jensen transformers are supposed to be better than the ones in lower cost boxes. As mentioned above, there are active and passive DI boxes. The active ones need a power source and can supply gain and sometimes processing features. (I have a BBE active box that includes their Sonic Maximizer.

Here is a wikipedia article that covers all the basics:
http://en.wikipedia.org/wiki/DI_box
The article also includes a picture of a 2-in-1 or stereo DI box.

Also the link above to the Whirlwind information is excellent. There are several versions of boxes at the end of the second article. There are some stereo ones, and one that are specifically made to go from a consumer output with RCA connectors to a pro device.
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Old May 11th, 2008, 01:35 PM   #12
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Good audio is not trivial.
Ty... You got that right. I try to look ahead when purchasing too, but sometimes I end up being penny-wise and pound-foolish.

I have no real idea what's coming from the track's board. Reading line level into the camera it doesn't sound bad, but it ain't great either. Specs? Who knows.

Thanks for the food for thought.
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Old May 11th, 2008, 01:47 PM   #13
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Take a look at this page on the Whirlwind site, especially their Direct-2 and Direct-2JT down near the bottom of the page if you need stereo. Still 1/4 inputs instead of XLR but adapters are readily available and cheap - Whirlwind makes good quality units.
Steve... Thanks for the link. The Direct-JT looks like it will work. At the price, I'm wondering if it's worth the money to upgrade to a field mixer to help "future-proof" me for other projects I don't even know about yet.
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Old May 11th, 2008, 02:21 PM   #14
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Steve... Thanks for the link. The Direct-JT looks like it will work. At the price, I'm wondering if it's worth the money to upgrade to a field mixer to help "future-proof" me for other projects I don't even know about yet.
Different tools for different purposes so it's not a simple linear progression and I can see situations where you might need both. For my money, the first priority would be a good mixer but you are talking a signifigant increase in expense over the DI box. Still, the mixer will solve a wider range of the problems you might encounter in different situations plus give you better control over your audio in general than you have now. The economics are such that it's way more economical in the long run to buy right at the very start rather than starting cheap and incrementally upgrading. Pro audio gear doesn't lose value the way other products do - you'll pay pretty close to the same price for a 5 year old Schoeps microphone (if it hasn't been terribly beaten around) as you would for a brand new one, for example.
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Old May 11th, 2008, 02:35 PM   #15
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Steve... Yeah, I see your point. I'll do some searching around on mixers and if I still have questions I'll start a new thread. I think a mixer's the way to go.
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