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Old May 10th, 2011, 08:18 AM   #1
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Distortion and AT897

I have an Audio-Technica AT897 that I used to capture a group of dancers with my XH-A1.
I used the AT897 with Phantom power (no battery) and it was set to Flat not Roll Off.
The sound was greatly distorted and the level meter in the camera didn't bounce around as normal but only changed up or down when I moved the volume control on the specific XH-A1 channel.
Should I have used a battery without Phantom or should I have adjusted to Roll Off?
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Old May 10th, 2011, 08:27 AM   #2
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Re: Distortion and AT897

Can you post a short sample of the problem audio?

There are a number of places in the audio chain that a problem could happen.

The sound of the performance could be EXTREMELY loud.
The mic may be damaged.
The mic cable may be damaged or incompatible with phantom power.
Phantom power from the camera may be damaged.
The mic input may be damaged.

However, the first place to look is whether the sound coming in to the mic input of the camera is simply overloading the input. This will cause overloading and distortion before the recording level control takes effect. To prevent this, use attenuation to reduce the signal coming into the camera's mic input.

Lastly the recording level may be set too high, but generally that can be recognized and corrected as you monitor with headphones and adjust the recording level during the recording.
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Old May 10th, 2011, 09:28 AM   #3
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Re: Distortion and AT897

Jay thanks for all the scenarios. As I mentioned before the phantom power channel that captured the AT897 never overpowered into the red BUT the bar never jumped back and forth and only moved when I changed the volume on the XH-A1. This lack of constant sound moving cannot be normal.
Included sound sample from the AT897 one channel.
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Old May 10th, 2011, 10:01 AM   #4
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Re: Distortion and AT897

http://www.dvinfo.net/forum/attachme...1&d=1305039653
Attached Files
File Type: wav AT897 Channel.wav (3.53 MB, 59 views)
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Old May 10th, 2011, 10:30 AM   #5
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Re: Distortion and AT897

This is a bad case of clipping, and it may well be that the sound level was greater than the mike can handle, as your description of the level indicator is typical of a maxed-out input.

You could try the -25dB pad on the camera input in such a situation, but if the mike itself is maxed out and sending a clipped signal, all you can do in the camera is make a less-loud distorted signal.

The waveform from your audio file (attached) is typical of an overloaded signal. The AT897 has a max level of 129 dB on phantom power and 115 dB on battery.
Attached Thumbnails
Distortion and AT897-clipping.jpg  
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Old May 10th, 2011, 11:16 AM   #6
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Re: Distortion and AT897

The camera's mic inputs also have -20db ATT attenuation switches which should usually be engaged when recording something loud. Also make sure the +12db mic gain is set to off.

The AT897 has a fairly low output for a condenser mic, but the camera's mic input is very sensitive as camera's go.
I would hope it wasn't so loud that it was overloading the mic on phantom power, however many shotgun mics can behave oddly if they are used near reflective surfaces and will begin to have distortion at lower levels than normal.

My bet is still on needing to attenuate the mic input on the camera.
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Old May 10th, 2011, 12:23 PM   #7
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Re: Distortion and AT897

I would concur with Jay, in live loud music situation, you should use an attenuator. I doubt the mic itself was overloaded and the very few extra dBs of headroom you gain between using Phantom pwr. vs. battery, would be negligible. (unless the battery is dead.. or close to it)
Like low-budget DARs, most digital camera's 'record volume control' only affect the digital audio level and does not prevent preamp/input stage overload.
Indeed, that particular camera does have a "Mic Att" switch. Try that the next time you're in a high SPL environment.
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