How To Test Mic's Low Frequency Roll Off Feature?

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XA10

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I recently purchased an Audio Technica BP4029 Stereo Shotgun Microphone. After playing around with it awhile, I'm noticing that its "low frequency roll off" feature has hardly any effect on the sound output. Is there a good and reliable way to test this feature to see whether it's working as it suppose to or that I got a defective unit? How do you test this feature?
 
It should be audible on voice tests, but if not, try it on something bassy.

If you don't have a bassy instrument to hand, pipe a sine wav out your speaker and record it with the mic.
Obviously mute the recorded track to prevent feedback.

Pick something good and low like <100hz. Toggle the switch over a few seconds then disarm and play it back.
You should hear a difference if it's working.
 
Steenamaroo said:
It should be audible on voice tests, but if not, try it on something bassy.

If you don't have a bassy instrument to hand, pipe a sine wav out your speaker and record it with the mic.
Obviously mute the recorded track to prevent feedback.

Pick something good and low like <100hz. Toggle the switch over a few seconds then disarm and play it back.
You should hear a difference if it's working.
Click to expand...

Thanks for your response. I do not have any bassy instrument or any speakers. What's the best way to do a voice test?
 
arcaxis said:
These are kind of exciting to mic up....:D
Click to expand...

Thanks for the links. Just went through them all. Here's another question: my mic's spec says "Low Frequency Roll-Off" at 80 Hz, does this mean that I should expect to hear the same degree of noise that I'm hearing in the linked test, "80hz - YouTube"? Or should I expect the roll-off point at 80 Hz to be quieter?
 
It means that sounds at 80hz and below will be reduced when you engage the filter.

It may not be very obvious with an 80hz tone, but it will become more obvious at the frequency decreases.

For example, the rolloff might reduce by 1db at 80hz, but maybe 4db at 70hz.
This curve just depends on the mic and what kind of filter the manufacturers used.

Keep in mind, this filter is't doing anything that you can't just do in software later.
Filters are built into mics for applications where live monitoring is important. Like a live concert or something.
 
Steenamaroo said:
It means that sounds at 80hz and below will be reduced when you engage the filter.

It may not be very obvious with an 80hz tone, but it will become more obvious at the frequency decreases.

For example, the rolloff might reduce by 1db at 80hz, but maybe 4db at 70hz.
This curve just depends on the mic and what kind of filter the manufacturers used.

Keep in mind, this filter is't doing anything that you can't just do in software later.
Filters are built into mics for applications where live monitoring is important. Like a live concert or something.
Click to expand...

When I tested the roll off feature, I did so by pointing the mic at the sound of my 55 gallon fish tank's motor, expecting that the roll off feature would quiet the sound. The results of recording with the roll off turned on and off, however, were almost identical. Is this normal and should be expected with the mic with the aforementioned roll off point of 80hz?
 
Well, if your fish tank is making a sound below 80hz you should hear a difference, and if it's not, you shouldn't.

80hz is getting close to the territory where you feel it rather than hear it.
You know in the cinema when you feel the explosion sounds through your chest? That's sub 80hz.

If I'm patronising you, then all apologies, but the human voice is usually focussed around 1000hz. Cymbals etc might be 6, 7, 8000khz and higher.
The boom of a kick drum might be around 100hz.

A fish tank motor might have a hum at a few hundred hz, but I doubt it would be good test material for a roll off filter.



Given that you don't have speakers, do the following.
Plug in your mic,
set up a session in your recording software,
arm the track so you can see a meter move up and down.

Now mute the microphone track in your software,
set the mic inside the cup of your headphones,
play a 60hz tone from youtube.

The meter should sit at a static level.

Engage the rolloff switch and observe again. With any luck the meters should read lower this time by a few db.
 
Steenamaroo said:
Well, if your fish tank is making a sound below 80hz you should hear a difference, and if it's not, you shouldn't.

80hz is getting close to the territory where you feel it rather than hear it.
You know in the cinema when you feel the explosion sounds through your chest? That's sub 80hz.

If I'm patronising you, then all apologies, but the human voice is usually focussed around 1000hz. Cymbals etc might be 6, 7, 8000khz and higher.
The boom of a kick drum might be around 100hz.

A fish tank motor might have a hum at a few hundred hz, but I doubt it would be good test material for a roll off filter.



Given that you don't have speakers, do the following.
Plug in your mic,
set up a session in your recording software,
arm the track so you can see a meter move up and down.

Now mute the microphone track in your software,
set the mic inside the cup of your headphones,
play a 60hz tone from youtube.

The meter should sit at a static level.

Engage the rolloff switch and observe again. With any luck the meters should read lower this time by a few db.
Click to expand...

Great, I'll do the test after lunch and get back to you with the results... Thanks!
 
About any mic with an extend low end I'd imagine just blowing at the mic or tapping it you should hear the effect of the filter.
 
If you are 'listening' with earphones, chances are their low frequency limit is higher than what the roll-off is cutting out. You could load a frequency analyzer plug-in to your DAW.
 
Steenamaroo said:
It may not be very obvious with an 80hz tone, but it will become more obvious at the frequency decreases.

For example, the rolloff might reduce by 1db at 80hz, but maybe 4db at 70hz.
Click to expand...

Okay, the test went successfully! At 60hz, the roll-off reduced the noise by 7db. My mind's at peace now. :listeningmusic: Thanks for all your help, much appreciated!!
 
XA10 said:
Okay, the test went successfully! At 60hz, the roll-off reduced the noise by 7db. My mind's at peace now. :listeningmusic: Thanks for all your help, much appreciated!!
Click to expand...

XA10 said:
Yea, I know. I'm good at making fun of myself. So, other than being entertained, do you have any contribution to my original question?
Click to expand...


Great!!! Cause I've been restraining myself all day -
for I think I would have gotten the ban hammer if I contributed. ;)
 
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