STEP THREE: SET THE HIGH-PASS FILTER

The high-pass fi lter, also known as a low-cut fi lter, is a function that’s often over-looked and dismissed by many fi eld recordists. In my opinion, it’s important to adjust this function properly in every location to give separation between the low frequencies of the location’s ambience and the low frequencies of the talent’s voice. This is not a “set-and-forget” function—and it’s defi nitely not a function for you to dismiss.

The high-pass fi lter’s job is to cut low frequencies. The higher you adjust in frequency the less bass or low sounds you’re allowing to enter your mixer.

Your mixer will come with either a stepped or sweepable high-pass fi lter. They do the same thing, except one is a dial, the other a three-way switch.

To correctly adjust a high-pass fi lter follow this simple procedure.

Setting a Stepped High-Pass Filter

Figure 4.16 Stepped high-pass fi lter, 20Hz to 140Hz

to 100Hz), you’re cutting or not allowing the frequencies below the selected frequency to be recorded. The talent’s voice will sound thinner if the high-pass is cutting into it.

You will fi nd that for men, the cut will be around 80–100Hz, and for woman, around 140–150Hz. Very rarely do I set the high-pass fi lter to 20Hz or off.

Switch back and forth as many times as necessary until you clearly hear where the high-pass fi lter is cutting. If the voice is not being touched, switch the high-pass fi lter to its highest setting (let’s say 140Hz) and again listen for thinning in the voice. Set the high-pass fi lter just below the low frequencies of the talent’s voice.

When the high-pass fi lter is set correctly, the talent’s voice will seem louder and more

“on top” of the ambience. This cutting of low frequencies that are not present in the tal-ent’s voice will result in less competition from the ambience, giving more separation and clarity to the voice .

High-pass fi lter: If the voice seems to fall into the ambience when you increase the high-pass fi lter, you have set it too high. Back it off one setting.

Setting a Sweepable High-Pass filter

Figure 4.17 Sweepable high-pass fi lter, 80Hz to 240Hz

Once again, when the high-pass fi lter is set correctly, the talent’s voice will seem louder and more “on top” of the ambience. This cutting of low frequencies that are not present in the voice will result in less competition from the ambience, giving more sepa-ration and clarity to the voice .

Exception to this rule! When offending low frequencies of ambience are equal to or louder than the voice’s low frequencies, you may fi nd it necessary to cut into the voice.

When you do this, focus your listening on the presence of the voice. If it seems to get clearer and or louder, don’t hesitate to cut higher than you’d expect.

If you’re having a tough time hearing the high-pass fi lter, here’s a simple test you can do that should make it clearer.

1. Plug a mic into XLR “Input 1.” Turn up the CH1 fader to 50 percent or 12 o’clock.

Even though the stepped high-pass fi lter works perfectly fi ne, I prefer a sweepable high-pass fi lter. You can be more accurate where you cut since the sweepable dial is in fi ner frequency increments.

Start with the dial completely to the left, and slowly sweep it up while listening for the fi lter to cut into the low frequencies of the talent’s voice. Set the fi lter just below where you hear the lows, or bottom, of the talent’s voice get weaker.

Figure 4.18 Adjusting the high-pass fi lter

settings (20Hz and 140Hz), or turn the rotary dial from hard left to hard right. You should hear the bassy rumble of the ambience become less. That is your high-pass fi lter at work. This is where you need to focus your listening when you are making adjustments with the high-pass fi lter.

It’s important that you clearly hear the change in the bass or low frequencies when you make an adjustment to the high-pass fi lter. Don’t just sort of hear it working. Take the time and practice. You’ll quickly tune your listening to the frequencies that your high-pass fi lter affects, and you’ll be able to use this function to its full potential.

This may sound complicated, but it’s not. You’ll soon be making the decision on where to set the high-pass fi lter in a matter of seconds.

High-Pass Filter Warning!

By ignoring the high-pass fi lter on your mixer, you are exposing yourself to a major disaster that low frequencies can infl ict on a recording. Do not think that by leaving the high-pass fi lter at its lowest setting (20Hz or off) you are Okay. Wrong!

At its lowest setting you are allowing low frequencies to enter the mixer, possibly overloading or distorting the pre-amp. The worst case is something called “false meter-ing.” This is when low frequencies that you can’t hear enter the mixer and indicate on the meters that you have the correct amount of input. You’ll fi nd you can’t increase the channel volume without distortion, even though the dialogue seems weak. I’ve been there, and it was a frustrated fl ip of the high-pass fi lter that fi xed the problem.

2. If the mic has a bass roll-off switch, make sure it’s in the “Off” position. (see fi gure 4.19)

3. Switch the high-pass fi lter to its lowest setting, “20Hz,” or if you have a sweepable rotary dial turn it completely left.

4. Turn your monitor volume up loud enough so you can clearly hear the bassy, rumbly low frequencies of the room you are in. It is best if no one is talking. Focus your listening on the bottom or lower sounds of the environment.

5. Switch the high-pass fi lter back and forth between the lowest and highest Figure 4.19 Step 2: The bass roll-off is off when

in the “—” position.

In the real world, low frequency ambi-ence is everywhere, and the high-pass fi lter will help you to control it.

You’ve now “dialed in” your mixer and are ready to record. With these three simple steps you’ve set your mixer properly for the location and the talent’s voice. Whether your mixer uses a pre-amp attenuator or channel gain, stepped or sweepable high-pass fi lters, PPM or VU meters, it’s an abso-lute must that you control the location’s low frequencies, allow only the perfect level of signal to enter your mixer’s pre-amps, and operate your mixer at unity.