Microphone Hi-Pass filter use
 

Let me ask some of the more learned audio folks, is it common practice to enable the 'Hi-Pass filter' on Condenser microphones when feeding into a mixer? Or, for that matter, directly into a camera? Let me first say, this is primarily for VOX recording, not music.

In the past, I've enabled the 80Hz Hi-Pass as a 'general rule', to address HVAC rumble and to catch and mitigate any low-frequency noise that might occur.

If, I think I need more, I'll 'double-up', using the 80 Hz setting on my SD-302 Mixer. Although, I'm not sure it works that way.

J.

Re: Microphone Hi-Pass filter use
 

If you are recording voice, then as a general rule, I think it's fine to use the 80 Hz high pass setting. There is very little voice energy down this low, so the filter shouldn't have an adverse result. And yes, it will get rid of a lot of room rumble from HVAC, nearby vehicular traffic, etc.

Remember that the filter does not abruptly remove all energy below 80 Hz. It removes progressively more energy as the frequency goes further below 80 Hz.

One additional number that's missing from your post is the "slope" of the filter. It might be as little as 6dB per octave, or 18 dB/octave or more. For example, a 6dB/octave filter will remove 6dB more signal at 40 Hz, compared to 80 Hz. It will remove another 6dB (a total of 12dB) at 20 Hz, compared to 80 Hz. An 18 dB/octave filter will remove 18dB more signal at 40 Hz, compared to 80 Hz. It will remove another 18dB (a total of 36dB) at 20 Hz, compared to 80 Hz.

Filters with a shallower slope (e.g. 6dB/octave) may sound a bit more natural. Filters with a steeper slope (e.g. 18dB/octave) will be more effective at removing room rumble.

Re: Microphone Hi-Pass filter use
 

Yes. Very common.

That's what it's for.

It works exactly that way. The two HPFs will add. That is, if your mic has an 80Hz 6 dB/octave filter, and your mixer has an 80Hz 12 dB/octave filter, the two together results in an 80Hz 18dB/octave filter.

I did exactly this a few weeks ago. Had to use a hotel room for interviews, and the room they assigned shared a wall with the air handler for the entire floor. A low rumble that you could feel as well as hear, because it was also pretty loud. It was... less than ideal. So I walked the room listening for room modes and found a spot where the rumble was less bad. I put the interviewee chair in that null. Then I enabled the filter on my mic, and on my mixer both. The results are good enough that I didn't feel the need to add even more EQ in post. Basically a nicely sharp cutoff at 80Hz. Producer was shocked and pleased by the sound in the rough edit (before any post), always a good thing.

Re: Microphone Hi-Pass filter use
 

The only minor detail is what happens at 80 Hz. In theory, the specified frequency is the "knee" of the curve, where the filter is down by 3dB. So if you cascade two 80 Hz HPFs, the result (in theory) would be down 6dB at 80 Hz. So this moves the theoretical knee frequency, where the filter response is -3dB, upward a bit above 80 Hz. But yes, with the above example, the filter response at 40 Hz would be down 18 dB lower than at 80 Hz.

Re: Microphone Hi-Pass filter use
 

Only a few men with VERY deep voices reach down to 80 Hz.

But many places out in the Real World have ambient, environmental noise prevalent down in that range.

Re: Microphone Hi-Pass filter use
 

Mr. Greg Miller...the microphone in question is an A-T 4053b, the specs state, "Low Frequency Roll-Off 80Hz High-Pass Filter, Switchable".

Digging a little deeper on the A-T website the A-T 4053b states, "Low Frequency Roll-Off, 80Hz, 12dB/Octave".

Regards,

J.

Re: Microphone Hi-Pass filter use
 

Is it better to 'filter or Pad' the audio signal at the beginning of the 'audio chain', in this case the microphone, rather then to try and address it in the 'Mixer'? It would seem to make sense, but I may not understand the unforeseen consequences further up the Gain Staging chain.

Looking back, the 'video' portion of my education was a cinch compared the audio. : )

Regards,

J.

Re: Microphone Hi-Pass filter use
 

Yes it can be better to filter or pad at the mic end as most of the time it puts the circuit before the pre-amp inside the mic so can prevent overloading before it gets to your mixer.

Re: Microphone Hi-Pass filter use
 

Yes. For perspective, 80 Hz is about the second E from the bottom of an 88 key piano. Another way to look at that is the 20th key from the left. Find a piano and play it. It's pretty low.

Re: Microphone Hi-Pass filter use
 

Messrs. Miller, Watson, Crowley & Nattrass...thank you for your thoughtful and technically astute responses.

As I always say, DVInfo is a wonderful resource.

Best regards,

J.

Re: Microphone Hi-Pass filter use
 

IIRC, the SD302 mixer also has a 160Hz low-cut filter setting. Use much the same as the 80Hz, but for higher pitched voices... A handy filter for female voices.

It wouldn't be right for many male voices, unless in extreme circumstances.

But, yes, for dialog in most circumstances it's appropriate to start at the mic with the 80Hz rolloff.

Re: Microphone Hi-Pass filter use
 

For dialogue I tend to leave the 80hz high pass on all the time either at the mic end if it has one or the mixer, a 160hz can be useful if you are having to try and record voices outside in the wind or where there may be lots of LF rumble from air con, distant traffic or other machinery etc.

Voices recorded with the 160hz filter can always be warmed up again in post by adding some LF at 160-250 hz.

Of course it all depends on the mic and the mixer that is being used as they all have slight variations as to the effect of their high pass filters and a decent pair of headphones is essential but you should also be able to see the effect of the filters by looking at your meters whilst just listening to the noise floor that is present.

Re: Microphone Hi-Pass filter use
 

Bearing in mind all that has been said above about dB per 8ve, knee etc (and I know we are talking recording voices and not music here), but one common pitfall when recording female voice and guitar (or just guitar) is to overlook how low an acoustic guitar actually goes - as it is technically a transposing instrument it sounds an octave lower than most people think with the lowest E string around 82Hz and not 165Hz.

Fortunately it is perfectly possible to convey a musical note from a low instrument without its fundamental frequency (although that may seem counter intuitive) as the harmonics are what gives the note its character, but it is worth remembering all the same when considering HP filter use as it may well affect the quality of the lowest notes.

Re: Microphone Hi-Pass filter use
 

For dialogue I tend to leave the 80hz high pass on all the time either at the mic end
- Same here. Doubling up the 80Hz filters increases the LF rolloff slightly on the 4053/302 combo.

Re: Microphone Hi-Pass filter use
 

Mr. Colin McDonald & Mr. Seth Bloombaum...The information on female voices and acoustic guitars is interesting and makes sense.

If I understand you correctly, 'female voices and acoustic guitars', for example, are situations where you might consider using a the 160 Hz Hi-Pass filter?

The SD-302 Mixer has limited (no pun intended) EQ features, which could lend itself to being a little heavy handed with filtering. But, as Mr. Natrass points out, you can 'warm-up' the audio in post. Which is good information.

My intent, however, is to keep things as simple as possible and get the best possible results, maybe not perfect, with little or no audio manipulation in Post. Hence the reason I'm trying to do as much as I can 'up-front' to record a clean signal.

The reason for that is I don't currently have an audio S/W application, nor would I really know how to use it, if I did. My NLE (Vegas Pro) has a rudimentary audio section, 'mixing board', certainly not sophisticated by any stretch.

J.

Re: Microphone Hi-Pass filter use
 

Using the HPF in production is a good idea for dialog as it can help with wind and handling noise biut most sound "tailoring" should be done in post rather than in the field. It;'s very difficult to "un-equalize": if your master was recorded with it if you later change your mind while listening in the more relaxed environment of the editing suite. Your original field recordings should be as pristine and un-tampered with as you can make them. The HPF is to prevent recording problems, not give you a certain sound.

Re: Microphone Hi-Pass filter use
 

I'd generally agree with what Steve wrote above.

The question for these roll-offs applied at the time of recording is: Is there meaningful signal below 80 (or 160) Hz. If there isn't, take advantage of these filters on the mic and mixer. They're there because LF noise below the frequency range of dialog is commonly encountered.

But, no, James; the use of an LF rolloff for acoustic guitars has gotten a little intertwined with the discussion, and guitar should be treated differently than dialog during recording.

For guitar, I'd suggest:
If you're in an environment that has LF noise, find another place to shoot, and/or, turn off HVAC, refrigerators, other sources of noise. Or maybe shoot at another time that isn't so noisy.

Use a different mic if you can mic voice and guitar separately. The guitar mic should *not* be rolled off, not in the mic, not in the mixer channel.

If invisible micing is required, a boom mic, hypercardoid or short shotgun would usually be tried first for guitar. This could be supplemented with lav for voice, but most lav positions will get a lot of LF off the guitar.

A lot of this kind of work is done with a performer lip-syncing to a studio recording, or some other recording that was done with visible mics, because it's frequently hard to get the recording you'd like to have when invisible micing is required. Not an insurmountable obstacle in many (not all!) circumstances, but specialized mics, multichannel recording, installation of invisible pickups in guitars, lavs hidden in hair instead of on the chest, all these techniques and more can come out.

So... why is it that you're concerned about the female voice / guitar combo? What would the actual shooting circumstances be?

Re: Microphone Hi-Pass filter use
 

Mr. Seth Bloombaum...nothing specific regarding 'the female voice / guitar combo', it was an example used during the discussion.

It interested me from the standpoint of a specific application for the use of the 160Hz HPF, i.e., female voices.

Neophytes, like me, are always interested in an example of when to use a particular 'adjustment/effect'.

Or, as in the case of the 'Guitar', when not to use an adjustment/effect.

I also realize these are 'guidelines', not hard and fast 'rules'. But, as I often say, you have to start somewhere. It also gives me another data point for my 'best practices' list in my head.

This thread will definitely be copied and pasted to my 'Audio File'. : )


Thank you.

J.

Re: Microphone Hi-Pass filter use
 

I'm not familiar with the term "S/W"
VP's audio capabilities are as (or more) sophisticated and intuitive than many (audio only) DAWs. It supports both DX and VST plug-ins with automation of most parameters. In addition, the architecture was always 32bit floating point, since Vegas 1 (which was audio only) long before 'SloTools' adopted it. It ain't perfect though and lacks in some areas. (side-chaining for instance)

Re: Microphone Hi-Pass filter use
 

Hope this isn't too far off topic, but Rick started it!

I too have been a Vegas user since V1, when it was about the only multitrack non-destructive audio editor for windows (PT was mac-only at the time).

I've been teaching the Adobe CC suite... but I have to say that Vegas ranks right up there and in some ways superior to Audition and the audio side of Premiere.

Premiere does have a nice Merge Clips on audio feature, that on a project with few takes will easily auto-sync double-system sound (if you have *some* sound on the cam). But for a larger project with 10s or 100s of clips you'd still want Plural Eyes.

Audition does have a cool ADR sync-up, that I've never used.

But day in and day out Vegas is fast, accurate, good sounding, and supports any kind of workflow you could want. In particular, Audition separates into two interfaces, waveform (destructive) editing and multitrack. Certain of the filters, like NR, must be applied applied destructively even in the multitrack interface. Sony's stock filters are very good, better IMO than Audition. And they all work non-destructively, in a single interface, with excellent tweakability.

But if you have to play well with others, Adobe CC has largely taken over the indie/corporate market here.

Re: Microphone Hi-Pass filter use
 

Mr. Rick Reineke...it's my abbreviation for 'Software'. Probably not correct.

J.

Re: Microphone Hi-Pass filter use
 

Although you should always aim to "get it right" in production, there is nothing wrong with tweaking things a little in post. Really deep rumbles can overload some mics and mic inputs, so 80 hz is a good start, but I often play around in post to see if I should cut more low end (eg at maybe 100 hz) or notch something out higher up - although I would go to iZotope RX for more involved stuff.

BTW: In post, EQ always sounds more natural when cutting, rather than boosting frequencies.

Re: Microphone Hi-Pass filter use
 

Mr. Rick Reineke and Mr. Seth Bloombaum ...As I mentioned earlier in the thread, I strive to obtain as clean an audio signal as possible 'up-front'.

To be fair to Vegas Pro (VP), I haven't delved very deeply into the 'audio features' within the software beyond adjusting overall levels up or down. My bad.

So, when I said the software's capability was 'rudimentary', that was a bad 'assumption' on my part.

My thinking was, a dedicated audio mixing software would be significantly more sophisticated than what came 'bundled' in VP. I'm sure that's true to a certain extent, but it doesn't diminish the capabilities of VP. I need to investigate and become more conversant in the use of the tools I have, rather than criticize.

The old adage, "A poor Craftsman blames his tools.", comes to mind. : )

The truth is, my audio skills are 'rudimentary', not the software application. I hope that clears up any misunderstanding.

Best regards,

J.

Re: Microphone Hi-Pass filter use
 

No problem James.

As you develop your post audio skills, you'll find Vegas is very capable. And, as a single tool that combines audio and video editing, it's very efficient, you can do both without any export/import rigamarole where you have to keep track of intermediate files.

In Adobe CC there are THREE different interfaces to learn, och. The audio side of Premiere, the Waveform editor, and the Multitrack editor. With different shortcut keys for common tasks like zooming in/out on the timeline. (Hm, there's probably a setting to get them to be the same, but I have to teach the standard interface, I think)

Vegas has very good versions of all the basic audio tools, though I've been a little confused over the years about Noise Reduction. At times it's come with Sony's Sound Forge, other times in Vegas, other times as a standalone product. It's great and occasionally very needed. And to finish the suite of audio tools, a mastering package like Izotope Ozone is very handy for music production. But what Vegas is capable of natively is excellent for audio-for-video.

An editor who is finishing his/her own work should be learning the uses of (dynamic range) compressors and parametric equalization. Those skills alone, combined with good monitoring, will make most projects shine.

Vegas also allows you to cut audio down to the sample level, unlike other NLEs that only cut down to the frame level. There's a big difference between 1/30th of a second and 1/48,000th of a second precision when you're concerned about breathes, clicks, and syllables.

Again, playing well with others can dictate the software you have to work on, but if you know post-audio in Vegas you have a whole bunch of skills that are transferable to any other software.

Re: Microphone Hi-Pass filter use
 

Thanks, Seth! I appreciate your thoughtful response.

Best regards,

J.

Re: Microphone Hi-Pass filter use
 

My thinking was, a dedicated audio mixing software would be significantly more sophisticated than what came 'bundled' in VP
> An external mix surface can be added to VP (same w/ PTs). The latest version of VP is bungled with over 35 mono / stereo / 5:1 plugins'. More if one also has Sound Forge Pro (recommended), OTOH, most pros have there own third-party favorites anyway (Waves for example). All things being equal, there would be no audible difference between PTs, Nuendo and VP.

Re: Microphone Hi-Pass filter use
 

Thanks, Rick! I appreciate your insight. BTW, I'm using VP v. 11.0.

Best regards,

J.

Re: Microphone Hi-Pass filter use
 

James, I know a guy who runs a recording studio based on a workstation running Vegas, so it's definitely capable enough. And yes, getting some chops with parametric eq and compression/limiting will serve you well. If you want to get fancy with regards to removal of unwanted sounds/noise, iZotope's RX4 is hard to beat. But it is a bit costly at around 350 list price, and takes some practicing to really master. Still, it has saved enough of my audio to make itself indispensable.

Re: Microphone Hi-Pass filter use
 

Thanks, Christian! The journey continues...

J.