Hi-
I recently worked on a documentary where we rented a hotel room to film some interviews. The producer went to the hotel room the day before. The room was a meeting room, and totally quiet. Great location, yes?

Well, the day of the filming, the air conditioning is roaring. At least, the hotel people told us the sound was air conditioning. It was very loud. It never went off the whole day.

We knew the sound was going to be effected, but we didn't have another location to go to, and cancelling all the interviews that day wasn't a good option.

The hotel folks didn't have another room to move us to (I think the AC was running in all of them anyway) and also refused to turn off the A/C.

So we recorded as planned, and we're going to try and clean up the sound as best we can.

No one reading this knows how loud the sound was, but I'm wondering if other people would have made the same call? Would you have said 'If the sound is going to be bad, then we're wasting our time. Film somewhere
else, or cancel for the day'?

We didn't have a mixer, would that have been helpful in such a situation?

If not for the AC, the place would have been perfect. Do other people film in hotels and do you ask if you can turn off the AC when needed?

...I often have to shoot interviews in offices where it's impossible to turn the AC off, so I try to minimize the AC noise through careful mic'ing.
( a good set of headphones will give you some idea of how bad the noise really is )

Can you post a small sample of the audio you recorded?
( I'm curious to see how much it can be cleaned up with software )

1. Plan the site better. You can sometimes find hotels that will work with you, but it is definitely rare.
2. Record with a good level. A low level will kill you in post.
3. WAVES, BIAS, Sony all have great noise reduction tools. Audition/SoundBooth have pretty good NR tools. If the AC is constant, you can usually bring it to a useful level, but you'd obviously have been better off w/out it.
Small budget in production usually means bigger budget in post.

A mixer might have helped in the decision process, but noise is noise. Either you find a way to deal with it or you don't shoot, IMO. The whole concept of "We'll fix it in post" is BS most of the time, again...IMO.

...I often have to shoot interviews in offices where it's impossible to turn the AC off, so I try to minimize the AC noise through careful mic'ing.
( a good set of headphones will give you some idea of how bad the noise really is )

Can you post a small sample of the audio you recorded?
( I'm curious to see how much it can be cleaned up with software )

Yeah, that's a good point. We tried to get the mics as close as possible, but maybe there was more to be done. We were trying to get a sound person at the last minute, but couldn't. I do alright when conditions are not too terrible, but I'm no professional sound recordist.

I can put up a sample, it will be a few hours from now, as I'm not near the equipment right now. Thanks for your offer.

1. Plan the site better. You can sometimes find hotels that will work with you, but it is definitely rare.
2. Record with a good level. A low level will kill you in post.
3. WAVES, BIAS, Sony all have great noise reduction tools. Audition/SoundBooth have pretty good NR tools. If the AC is constant, you can usually bring it to a useful level, but you'd obviously have been better off w/out it.
Small budget in production usually means bigger budget in post.


Thanks - I'm thinking from now on, we will at least ask a hotel (or wherever we are recording) if we can control the thermostat or AC. But it seems like a lot of places do not have that option.

At least one of the speakers I think we got good levels, but they could have been better.

The only 'plus', if it can be called that, is that the AC is constant - boy is it constant.

I can put up a sample, it will be a few hours from now, as I'm not near the equipment right now. Thanks for your offer.

If you can, try to include a sample of just the AC by itself ( no one is talking for a few seconds ), which will make it easier to determine how to filter it out.

Aside from getting the best sound possible in production (IE: A dedicated sound recordist monitoring the set) - getting the mics close, possibly using a bass roll-off depending on the quality of the noise - all you can hope for is to get the system turned off.

Most systems in large building are controlled by a central thermostat, and that's why they are loathe to sacrifice the air in other rooms to accomodate your room.

If you can't get the system turned off , you CAN do a few things to dampen it on site. There are two sources for AC noise - mechanical and airflow.

The mechanical sound - the sound of the ac compressor clicking on or the fan running, is usually generated from another room, or from a rooftop above. It reaches the room through vibrations in the wall and ac ducts. Not much can be done to minimize that sound.

The sound of the AIRFLOW - that is the sound of air hissing through the grates/vents can be mitigated in a number of fashions. IF you can adjust the vent, try that first. CLOSING the vent completely can silense the airflow, but only if you can close it completely. (This might have the added bonus of eliminating some of the mechanical noise that might be channeled up the vents.) Most vents won't close completely however, and by minimizing the airflow, you might actually increase the 'hiss'. SO try OPENING it completely.

Point is, adjust it for most silent operation. Also consider BLOCKING the airflow with furni-pads. Every good grip kit should have one or two. I've used furniture pads dangeling in front of ac vents or refrigerators that couldn't be turned off before. It helps some, and as Douglas points out, anything you can do in production is going to save you time and money in post.

Thanks for everyone's suggestions. We've taped a couple of interviews in office-like situations, and we've never had this much of a problem with background noise.

Richard's tips on dealing AC are very good, me thinks.

Quick question - sort of on topic, sort of not -

Just furniture pads that you would buy from a moving company or are there specific sound reduction blankets available?

Thanks,
Kevin

Quick question - sort of on topic, sort of not -

Just furniture pads that you would buy from a moving company or are there specific sound reduction blankets available?

Thanks,
Kevin

You can get special sound blankets but regular furniture pads work just as well, just maybe not as glamorous, and a LOT cheaper.

I've never been glamorous... ;)

... and I've always been cheap. But that doesn't mean I'm EASY!!

FurniPads are a staple in grip kits. Mostly for protecting surfaces just like movers do. Lots of times you want to cover furniture in locations if you have to haul equipment around. ESPECIALLY if you don't own the nice furniture and you want to shoot there again. And yes, they can double as sound baffles, and stunt pads, and sleeping pallets and ... well, never mind.

Hi Dennis:

Please tell me that you were a smart boy and recorded with a lav and a boom as everyone should everytime possible?

If you did, you should find that the lav will have a LOT less of the offending noise than the boom.

Personally, I use SoundSoap Pro from Bias, it's pretty good although the WAVES Restoration bundle is better. Neither will completely eliminate your noise but both can bring it down to a tolerable level. Will your interviews have music behind them? Musc, even low in the mix, can mask a lot of ambient noise.

If you only recorded with a boom, you are learning a painful lesson. ALWAYS mic interviews with both boom and lav. More often than not, the lav will save your rear in these situations.

BTW, I shoot interviews in hotel rooms all of the time, not to mention at offices at the movie studios where the AC controls the whole floor so it cannot be shut off. This is a common problem. Some extra C-stands and sound blankets/furni pads would have saved your rear, learn from that and next time bring them.

We've all been where you are, best of luck,

Dan

Don't expect sound blankets to work miracles either...they are NOT broad band absorbers. They do not provide any isolation from low frequency mechanical noise.

Always record :30 of room tone at the end of the shoot for having the ability to use noise reduction software to lower the offending noise.

On several occassions I have been involved in recording interviews with a constant noise wether it be a air conditioner or a furnace or refrigrator. One thing I always consider is what is the subject matter of my story. On several occassions I have looked for a sound that will drowned out the constant annoying sound and also fit in with my subject matter. In one instance the air conditioner was non stop and we moved our talent over to the window and opened the window so we could here the traffic in the background instead of the air conditioner. We placed a hypercardoid 5 inches from the talent facing away from the traffic and placed a omni directional toward the traffic. Mixing the 2 together gave the interview a great quality that fit the story and the traffic noise was very much like the score to the piece. There have been times we have used a bird feeder(birds chirping), water running, television, radio, and also train rumbling. It works fairly well if the mix is unintrusive to the words being spoken.

Hi Dennis:

Please tell me that you were a smart boy and recorded with a lav and a boom as everyone should everytime possible?

If you did, you should find that the lav will have a LOT less of the offending noise than the boom.

Dan

Thanks, and yes we did both lav and boom. The lav channel is a bit better, but not that much to my ears. But another point in our favor. Just yesterday I was thinking, 'oh yeah, should have used c-stands and blankets'.

We also recorded (as we always do) a good 40 seconds of room tone, for each interview since we re-arranged the background.

Had to tell people you can't talk AND you can't sniffle! OR snort! OR cough! OR fart! Don't breath for crissakes, you can do that later!

I'm going to put up a sample of the audio for those interested, didn't get to it yesterday.

I have Adobe Audition 2.0, and was playing around with the noise reduction. It didn't clean up the sound to my satisfaction, so I'm thinking we will just have to re-interview people.

I've seen a lot of references to SoundSoap - Would you guys say more effective than Audition? I've seen SoundSoap 2.1 and SoundSoap Pro on the Bias website. Quite a price difference - is SoundSoap Pro much better at noise reduction, anyone know?

I have Adobe Audition 2.0, and was playing around with the noise reduction. It didn't clean up the sound to my satisfaction, so I'm thinking we will just have to re-interview people.

Hey Dennis,

I've had pretty good success with the Sony Noise Reduction plug-in 2.x ( now part of Sound Forge 9 ) the past couple of years. If you could post a sample of your audio, I'll see what I can cook up. If I'm happy with it, I'll send you the results to check out.

I've seen a lot of references to SoundSoap - Would you guys say more effective than Audition? I've seen SoundSoap 2.1 and SoundSoap Pro on the Bias website. Quite a price difference - is SoundSoap Pro much better at noise reduction, anyone know?

Yes, there's a big difference between the pro and non-pro versions, though I do most of my clean-up with the Sony NR tool because I find it easier to use ( in either Sound Forge or Vegas ) than the SSoap user interface.

Hey Dennis,

I've had pretty good success with the Sony Noise Reduction plug-in 2.x ( now part of Sound Forge 9 ) the past couple of years. If you could post a sample of your audio, I'll see what I can cook up. If I'm happy with it, I'll send you the results to check out.


Thanks, I will. I meant to do it yesterday, but didn't have time. In the next day, I definitely will.

Here it is. It's about 60 seconds long, the first 30 seconds is just the room tone. The last 30 seconds is the person talking, of course.

http://www.catzillaproductions.com/Shared/Beth1.wav

It's uncompressed from Premiere Pro, but it's only 10 MB. One channel is the lav, the other is the shotgun. Well, that's how it was recorded, I'm not sure if that's preserved in the export.

Hi Dennis,

I took a quick stab at it using Sound Forge 9. Here is what I did to process your file:

- Split the channels, and decided that the right channel ( probably your lav ) was more useable.

- Ran DC Offset just in case.

- Minus 21 dB RMS normalization

- 3 and 4 passes with the Sony Noise Reduction plug-in. Made a noise print for each pass, then processed the audio at -6 dB in Mode 2.

- Tried a little Paragraphic EQ at -5 dB at 4,825 Hz wide 2.5 octave to try to smooth out the midrange a bit.

Here's a MediaFire link to check things out:

http://www.mediafire.com/?4kqckzgz12l

...Let me know what you think.

- Guy

Wow. That is awesome. I thought Beth1R_4pass.wav was best. I used the NR tool in Audition on that.

Comparing Before and After is pretty incredible. Bravo, sir! Bravo!

I also know about mediafire now. I put my version (based on your version) here for you to listen -
http://www.mediafire.com/?1sqjtb0ezby

Guy,
That Beth 1r 4 pass is great. Can you provide more details. I use Waves Restoration and it's common to get the artifacts like those heard in Dennis' version. A screen shot of your set-up would be helpful to correlate Sony's setting to Waves. Why RMS normalization? What is Sony's "Mode 2"? Why 6db under?

The key must be the multiple passes with gentle NR each pass. Process time would take a while especially on large file, but the results are fantastic. Good Job.

Wow. That is awesome. I thought Beth1R_4pass.wav was best.

Yeah, I thought so too, though I was doing this from a client's office with the client's crappy $30 Sennheiser DJ headphones, so I wasn't a hundred percent sure I was hearing the real thing. Beth's voice was sounding a little nasal, which might be her natural voice, which is why I tried using the Paragraphic EQ to hide this quality.

I used the NR tool in Audition on that.
Comparing Before and After is pretty incredible. Bravo, sir! Bravo!

Thanks. It's the process of trying to figure out how much NR to apply is the hardest aspect for me. If you don't do enough, the noise will still be front and centre. Go too far, and noticeable distortion starts to creep in.

I also know about mediafire now. I put my version (based on your version) here for you to listen -
http://www.mediafire.com/?1sqjtb0ezby

...Please don't take this the wrong way, it's possible that it's my equipment isn't reproducing things correctly ( I'm at home now using my Sony 7506's ), but I'm getting some clipping distortion when Beth speaks loudly, like when she says the phrase "Our organization". Visually the top of the sine wave also looks clipped too, so you might want to sort this out.

Also, it sounds like Audition is using a noise-gate which definitely helps to lower the noise floor, but I find it can draw attention to itself unless there's a music or ambience track to hide when the "noise floor drops out". ( i.e. Suddenly it's too quiet )

...Well, I hope this helps to save you from a reshoot. It certainly looks possible to fix your noise in post.

Cool stuff.


- Guy

Guy,
That Beth 1r 4 pass is great. Can you provide more details.

Sure thing. Though I don't know how much of this will translate unless you are using Sony Sound Forge with the NR 2.0 plug-in. ( now included with SF9 )

I use Waves Restoration and it's common to get the artifacts like those heard in Dennis' version.

What I like about Sony's SF is that I can apply each effect seperately, and use my own judgement on how happy I am with the results. I don't know Waves Restoration at all, but hopefully it's not too automated, so you can apply effects one at a time, and check your results as you go.

A screen shot of your set-up would be helpful to correlate Sony's setting to Waves.

You'll have to let me know how successful you were at translating them.

Why RMS normalization?

Root Mean Square Normalization, which is supposed to be a better representation of the overall "power" of the recorded sound file. I find that the standard Peak Normalization can sometimes really distort the volume of an audio file, unless you manually correct this afterwards. RMS Norm isn't perfect either, but I like it's effect more than Peak Norm.

What is Sony's "Mode 2"?

Sony's Noise Reduction 2.0 plug-in offers four modes of NR, which are essentially the strength of the NR effect. Mode 0 is brute-force, while Mode 3 can be quite gentle. Mode 2 is the default, which generally does a good job. I think of this like choosing coarse sandpaper versus a very fine sandpaper. The finer stuff often works better, but takes longer to get the job done. :-)

Why 6db under?

This is the Noise Reduction effect in dB. You are less likely to "bork" an audio recording by correcting things in multiple passes, especially if you make a noise-print of the noise you are trying to get rid of with each pass. Remember the sandpaper thing?

The key must be the multiple passes with gentle NR each pass. Process time would take a while especially on large file, but the results are fantastic. Good Job.

Yeah, I'm a better audio doctor with a scalpel, than I am with a machete. <g>

Screenshots of the key SoundForge 9 Effects I Used
http://www.mediafire.com/?ctvmtw4999j


- Guy

Thanks for the screen shot. So are you normalizing to RMS value to get the overall level up before you begin the the NR process? It is probably better than peak normalization since one spike can really throw they whole level off.

When you are sampling the noise how long is the sample? Typically I will use a fraction of a second.

I know what you mean about the difficulty of how much processing to use. The temptation in the process, at least for me, is to try to go too far in one pass. This creates the distortion or mechanical sound..

I am going to play around with mutiple passes and see if I can get close to your incredible results.

For fun I have included a Waves X-Noise screen shot.

...Please don't take this the wrong way, it's possible that it's my equipment isn't reproducing things correctly ( I'm at home now using my Sony 7506's ), but I'm getting some clipping distortion when Beth speaks loudly, like when she says the phrase "Our organization". Visually the top of the sine wave also looks clipped too, so you might want to sort this out.

Also, it sounds like Audition is using a noise-gate which definitely helps to lower the noise floor, but I find it can draw attention to itself unless there's a music or ambience track to hide when the "noise floor drops out". ( i.e. Suddenly it's too quiet )

...Well, I hope this helps to save you from a reshoot. It certainly looks possible to fix your noise in post.

Cool stuff.


- Guy

Yeah, it certainly isn't perfect, but from where it was before, it's much better. Hopefully I can duplicate what you did in my copy of Audition.

When you are sampling the noise how long is the sample? Typically I will use a fraction of a second.


How does the length of the noise sample effect the process? Is it better to do a very short sample, then apply Noise Reduction?

Would a smaller sample take out a smaller piece, so less destructive to the dialog? Then you take another tiny sample, apply NR, and repeat until you get to where you like it?

So are you normalizing to RMS value to get the overall level up before you begin the the NR process?

Yes. I don't know if it's better to the NR first or the normalizing, but I figured that it would be easier for me to hear the subtleties of the NR effect if I did my usual audio processing first.

It is probably better than peak normalization since one spike can really throw they whole level off.

In theory yes. RMS normalization is still effected by audio spikes, just to a lesser degree than Peak Norm.

When you are sampling the noise how long is the sample? Typically I will use a fraction of a second.

I used almost all of the sample that Dennis provided, figuring that it would guarantee a good sampling of all of the noise frequencies that needed to be taken care of by the noise-print process. I think one second would be as effective provided the noise is very consistant. The AC unit seemed to be a steady drone.

The temptation in the process, at least for me, is to try to go too far in one pass. This creates the distortion or mechanical sound.

Yeah, as soon as I start to hear that metalic "phlanging" I know I've taken things too far.

I am going to play around with mutiple passes and see if I can get close to your incredible results.

It would be great if you could describe what your process is, so we'll have a recipe on file for Waves Restoration too.

For fun I have included a Waves X-Noise screen shot.

A lot prettier than Sound Forge, but I think that's a Mac thing. Most Mac apps seem to have better looking UIs.


- Guy

How does the length of the noise sample effect the process? Is it better to do a very short sample, then apply Noise Reduction?

Would a smaller sample take out a smaller piece, so less destructive to the dialog? Then you take another tiny sample, apply NR, and repeat until you get to where you like it?

Yes, yes, yes and yes.

Add one step - each time you take a noise sample you have some settings you can apply to the NR based on that particular capture. Doing multiple caps and filters is good technique, but you should have a light hand with the NR settings for each sample.

Also, Sony NR offers a checkbox for "keep residual" This is worth selecting and listening to, as it will preview what's being thrown away. If you hear some voice-like sound either back off on the settings or take a new sample until you are hearing and throwing away noise only. (don't forget to uncheck "keep residual" when you're done!)

One more note: Sony NR is a direct-x plugin that also appears in Vegas, and probably in other sound apps that use direct-x plugins (but I've only used it with Sound Forge & Vegas).

You will need a mixer for this to work. You need to have one mike wired out of phase acoustically from the mike or 2 mikes you are picking up dialog with.

You point the out of phase mike directly at the offending noise source.
First set the gain of the dialog mikes so you are getting normal recording level on the mixers meter. If you are using a stereo mixer set the pan switches or pots for all of the mikes to either the left or right; they all need to be feeding the same buss.

To make the magic happen adjust the gain on the mike pointed at the noise source until you get maximum cancellation of the of the unwanted noise in the dialog mikes sound. To pull this off the audio operator must use a pair of good headphones that block outside sounds.

What you are doing is cancelling out the noise with the out of phase mike that is pointed at the noise source. The mike pointed at the noise source does not need to be the same type or manufacture as the dialog mike or mikes. They must be wired as balanced low impedance in order to reverse the
the acoustic phasing.

Let me know if you need to know how to know how to check mikes for phasing. it is easy if you have a mixer, either mono or stereo.
Using noise reduction in an editing program will not give the same degree of cancellation.

Hi Dennis:Please tell me that you were a smart boy and recorded with a lav and a boom as everyone should everytime possible?

If you did, you should find that the lav will have a LOT less of the offending noise than the boom. Dan

Hello Dan,

Sorry, but I have to disagree with you on several points.

Split tracking boom and lav doesn't buy you anything unless you aren't sure what you're doing or don't plan to have a qualified sound person listening to audio as its being recorded. If that's the case, split tracking still doesn't guarantee you good audio.

I don't know what your own situations have been, but in the vast majority of cases (not to say there aren't exceptions) for interiors, the right hypercardioid on a boom placed at the edge of the frame beats an omni lav, provided you are able to get within 12-18 inches from the mouth of the person speaking. In this situation, the hyper wins especially as the ambient noise increases. Unless there aren't any mitigating factors, the boom mic wins.

If you can't get that close because of the shot, then lavs MAY win. Again, a LOT depends on the acoustical and noise of the location.

If the rest of the shoot requires the talent to be on a wireless lav, you might as well start that way, just to ensure continuity of sound.

BTW, some folks think a shotgun mic is the only mic to boom with. That's wrong. A good hypercardioid works much better for interiors.

Regards,

Ty Ford

You will need a mixer for this to work. You need to have one mike wired out of phase acoustically from the mike or 2 mikes you are picking up dialog with.

You point the out of phase mike directly at the offending noise source.
First set the gain of the dialog mikes so you are getting normal recording level on the mixers meter. If you are using a stereo mixer set the pan switches or pots for all of the mikes to either the left or right; they all need to be feeding the same buss.

To make the magic happen adjust the gain on the mike pointed at the noise source until you get maximum cancellation of the of the unwanted noise in the dialog mikes sound. To pull this off the audio operator must use a pair of good headphones that block outside sounds.

What you are doing is cancelling out the noise with the out of phase mike that is pointed at the noise source. The mike pointed at the noise source does not need to be the same type or manufacture as the dialog mike or mikes. They must be wired as balanced low impedance in order to reverse the
the acoustic phasing.

Let me know if you need to know how to know how to check mikes for phasing. it is easy if you have a mixer, either mono or stereo.
Using noise reduction in an editing program will not give the same degree of cancellation.

Thanks! I would need to know how to check mikes for phasing. I'd also need to get a mixer, since I have one now.

I don't have a mixer either. I've hesitated to get one, since I wasn't sure how beneficial it would be. But it sounds like here it would have been great, if I knew what I was doing!

Some of our interviews are about very sensitive topics, so my fear is to lose something very valuable because the AC was really loud.

For low frequencies, yes. For HVAC hiss, not so much.

Regards,

Ty

Following Bill Wilson's reverse phased mic idea, Hosa makes an inline XLR reverse phase adapter, in case your mixer doesn't offer this.

Hosa Audio Adapter XLR Female to XLR Male Polarity Cross Phase Reverser
http://www.bhphotovideo.com/c/product/408146-REG/Hosa_GXX195_Audio_Adapter_XLR_Female.html


- Guy

Isn't the phase reversal trick basically the same thing the sound cancellation earphones do?

Simply put, is the idea to mic the noise, invert it, and add it into the sound from the other two mic so it effectively cancels out the noise being picked up by the "real" mic(s)

I think all three mics would need to be pretty close to each other so you don't get time lag between the positive and negative noise

Unless I'm missing something (quite possible) couldn't you just record a track with the noise and then invert the signal in your audio software and mix it with the "good" tracks?

Also, wouldn't there be some cancellation of the dialog to the extent that it was picked up on the "noise" mic?

Bill states that the results are better when the NC is done when you are shooting. I haven't tried this, but it sounds like it could work quite well with a directional mic so you avoid killing your dialog.

Isn't the phase reversal trick basically the same thing the sound cancellation earphones do?

Simply put, is the idea to mic the noise, invert it, and add it into the sound from the other two mic so it effectively cancels out the noise being picked up by the "real" mic(s)

I think all three mics would need to be pretty close to each other so you don't get time lag between the positive and negative noise

Unless I'm missing something (quite possible) couldn't you just record a track with the noise and then invert the signal in your audio software and mix it with the "good" tracks?

Also, wouldn't there be some cancellation of the dialog to the extent that it was picked up on the "noise" mic?


Persactly. NCI Miami shows us things that really can't be done.

Regards,

Ty

How would you compare the capabilities of the 2?

Thanks