Help please. I recently purchased a Sound Devices 302 Mixer, but it appears the High-Pass Filters are not working in either the 80 or the 160 setting. I leave near an expressway and I opened the window and recorded 10 seconds with no filter, 10 seconds at the 80 setting and 10 seconds at the 160 setting - as the tech and Sound Devices suggested. I tested it using all 3 channels – right and left and it all sounds the same. I even ran a fan and did the same test all over again and it all sounds the same. I'm using a Seinheiser me66 mikes with the switch turned away from the low cut.

According to the Sound Devices technician, I should hear a difference. Shouldn’t the hum of the fan or the rumble of the traffic be diminished when using the filters? Or am I misconstruing the function of the filters? If not, what are they for? Thank you.

The filter should and will cut 'low' frequencies. A fan might be noisy but not in the lows. This filter is there for a) lowering boom handling noises, lowering unnecessary low frequencies that might unduly effect the built-in limiters etc.

Please test again and listen only to what happens to the low frequencies. You should clearly hear it working.

Thanks for the info. The tech at Sound Devices said I should hear a noticble difference in the following sounds when the filter is used:

1) Fan or Air conditioning
2) Rumbling noise from highway traffic
3) Thumping noise from movement of the microphone

I did notice a difference in #3 but not #1 or #2.

I find it strange that all channels exhibit the same... Maybe the mic your using does not pick up the low-end enough to hear the difference.
Try using an LF oscillator to retest.
FYI: The 302 HP filters are not as steep as some other mixers like the Shure FP series.

I tried using a Sennheiser lav and got the same results. I did hear a difference if the mike is thumped or bumped, but I had hoped the filter would do more then just diminish thumping noises. My sound person tested her Shure mixer and I heard a distinct difference - my voice even sounded thinner.

What is the 80 setting as opposed to the 160 setting supposed to do?

80 means the frequence is cut (gradually) off at 80 hz which is lower than 160hz. In other words the 'effect' is stronger in the 160 setting.

But again, the main reason of using this filter is to keep mic/boom rumble and low frequencies away from the limiter.

Sooner or later you're going to edit your footage I suppose and here you can simply EQ any way you want.......

I personally never use a '160' setting, 80 maybe in certain situations because it is much easier to do that in post and one can also make better decisions there if this is a good idea. Once cut it's gone....


For film work I do a cut at 40hz - if at all. Also please don't forget that headphones do sound different than speakers.......and of course there are also all kinds of speakers.....;-)

Thanks guys. I appreciate the info. I guess the cars hitting the pavement didn't have enough bass and my fan must be an alto instead of a baritone. I obviously misinterpreted the function of the 302's filters but I still go back to the tech person saying I should hear a difference. I guess I have to assume then that it can't cut the hum of traffic or a fan.

Many lavs' have a frequency response that you would not hear a difference.
To repeat myself, the Shure has an aggressive LF roll off... To steep (18-24dB per octave) and too high (150Hz.) to be of much use IMO.
Cheers, R

Well here's what you do, SD says the low pass filters take several seconds to kick in so be sure to give time for them to activate. This is so you can use them while recording without any pops entering your audio. So back to what you can do...record without any high-pass, then record with 80, then record with 160...giving about 10 seconds after activating the switch so that it can be fully active. Then look at the audio samples in your eq filter in some audio application and you will most likely see a difference in the audio spectrum in the various hz range. Let us know the results. Oh and be sure its the same sound source, I assume traffic noise should be relatively consistent over the time frame you'd gather your samples.

From the manual, I believe the SD302 is 12dB per octave...so not nearly as aggressive as the shure.