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Old May 21st, 2008, 11:01 AM   #1
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In-Car audio for racing

Hi,

I'm looking for a better way to control the mic level on my in-car video setup. I am considering adding a compressor/limiter in an attempt to keep the audio from clipping. The problem is the mics can handle the SPL but the recorder just doesn't have the dynamic range to handle the car at full throttle/speed and I can't get the sound I'm after.

I have been looking at this as a solution - http://www.rolls.com/products/cl151.php

It looks small (important) and can be powered from 12vDC (also important).

Thoughts or alternatives?
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Old May 21st, 2008, 11:50 AM   #2
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How about a passive pad? One example is the Shure A15AS.
http://shure.com/ProAudio/Products/A..._A15AS_content

As long as you avoid clipping, you should be able to apply compression in post as needed.

From my experience, in-car audio only has to worry about the range from loud to super loud. A pad should do the trick. You'd only need a compressor in the car if you also need to capture soft sounds, and don't want to mess with the gain manually.
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Old May 21st, 2008, 12:34 PM   #3
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Thanks Jon,

A pad unfortunately won't work by itself. The reason why is I'm going to have to use a stand alone mic and not take the audio from the camera (it has a fixed preamp and isn't set up for SPL this high). The video recorder has line level input so I need a preamp of some kind to get from mic to line level.

I thought this would cover both bases. Give me a preamp and a limiter to help keep things in check.

I really wish a pad would work. For sure the low pain option.
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Old May 21st, 2008, 12:41 PM   #4
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Chris,
There is a very effective method you can use to effectively double the dynamic range of your recorder. Feed the mic to both the L and R lines; apply a db pad of your choosing to one, and leave the other alone. In post, pan between the padded signal and the untouched signal to keep everything in check.
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Old May 22nd, 2008, 04:10 PM   #5
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Quote:
Originally Posted by Chris Medico View Post
Hi,

I'm looking for a better way to control the mic level on my in-car video setup. I am considering adding a compressor/limiter in an attempt to keep the audio from clipping. The problem is the mics can handle the SPL but the recorder just doesn't have the dynamic range to handle the car at full throttle/speed and I can't get the sound I'm after.

I have been looking at this as a solution - http://www.rolls.com/products/cl151.php

It looks small (important) and can be powered from 12vDC (also important).

Thoughts or alternatives?
Chris:

Very interesting. Im just now figuring out how to capture the loud spls associated with some of my motorsports video. Nothing like an in-car scenario though.

Keep us posted.
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Old May 22nd, 2008, 04:42 PM   #6
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For loud SPLs, you have to attenuate before it reaches the A/D converter or you'll overload the A/D converter. The only way to do this is to use one of the many in-line attenuators. Shure makes some, Audio-Technica makes some, and whirlwind (and others) also make some. You have to be careful though because in these types of situations you could very easily overload the mic. Make sure the SPL limit on the microphone is within the limit you think you'll need. In one extreme case, I had to use an in-line attenuator at -30 dB AND set the attenuator on the Deva for -15 dB. That's a lot of attenuation and under most circumstances this would not be something you would ever want to do. The nice thing about the Shure and AT attenuators is they both allow you to switch the attenuation level with a manual switch.

Wayne
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Old May 22nd, 2008, 08:55 PM   #7
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Thanks for all the great advice!

One of the things that I need for this application is a preamp. The recorder that I'm using is a video recorder with line level inputs. If I had mic level inputs then for sure a simple pad would be all I need. Unfortunately, that is not the case.

The mic that is built into the camera I use has a preamp to line level but no gain control. The cameras are POV cameras and the mic gain is fixed expecting voice or at most the wind of a mountain bike (and not a 800hp Viper with a very open exhaust doing 175mph). With this setup as soon as they roll out of the pits and hit the gas the audio input to the recorder is saturated.

Now, My plan is to use a good friends high SPL mic and the box referenced in the first post to give me a preamp, some gain control, and maybe even some limiting for those times when I don't do the best job of setting the gain. This box also has a 5 segment input meeter which I see could be helpful since the recorder has no audio indication at all.

Something I am very curious to know is has anyone used one of these boxes or anything from this company? Any opinions if its total junk or OK?
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