Acoustic Pressure Measurement & What Pressure Sounds Like

In a recent Google Hangout I got together a bunch of experienced and talented audio engineers to help bridge the gap between what you are hearing as an engineer and how the room is causing that problem. We tried to cut through some of the confusion between “mix sound” and “room sound”. The following video and transcript comes from one particular section where we addressed the question “Acoustic Pressure Measurement”. If you would like to see the full hour and a half discussion you can see the video further down the page.

Brad Pierce (BP): I run Starfleet Audio which is in New England, Worcester County, Massachusetts, and I first started following Dennis about a year ago. I’m watching his videos and he’s talking about room acoustics and that’s certainly an area that I’m very interested in along with audio engineering. So he’s trying to bridge the gap from acoustic engineer to audio engineer and a lot of people out there doing engineering are new to the acoustic room kind of area and what Dennis has been trying to do is kind of bridge the gap with terminology and awareness.

A lot of us are typically gear pigs and we go out, we buy new gear because it’s easy and quick certainly but the harder point of mixing in a room is obviously the room treatment and mixing on headphones can be okay but there’s really nothing like mixing in a room with studio monitors. A lot goes on in the room when you mix like that or track even mastering as well. So one thing I thought of doing was something that was inexpensive and easy to do for people at home to see how their rooms react and the first test would be a like a pressure zone experience so that you can actually kind of hear the different pressure zones in the room, it’s very easy to do.

You can set up a sound wave and playback the certain frequency. I probably want to start in the 60 Hz to 300 Hz cycle area. We all know that that’s a very tough region to get right when doing mixing and you would play that single frequency on your monitors and then move yourself around the room and hear how the changes in level happen in your room and that is actually how you’re experiencing the different pressures zones within the room. So when you play complex waveforms like music back on your monitors, all that stuff is happening in all kinds of different frequencies with the harmonics and they’re interacting and so you can see how complex it does get. So room treatment really is the only way to get that right and of course Dennis has some great products in his lineup to help treat those issues.

Dennis Foley (DF): It’s amazing, I wish we could put together a chart to help people with exactly what you just said Brad because if you walk around the room and you notice pressure is maybe +3 / +4 / +5 over baseline that +3, +4, +5 means you’re not hearing X, Y or Z in that area of the room and I think, I don’t know quite how to do that yet but we’re definitely working on that because every increase in pressure means a decrease in perception. So I’m trying to figure out how to do that for people because it’s really critical and it’s just so hard to explain and this is the issue that we’re dealing with.

When Joshua came here to my studio, you know he’s been in music for years and years and years, but he heard things that he never heard before and it’s those things that we need to kind of quantify for people and it’s good that we’re talking about it. Maybe through all this talking and discussion we’ll figure out a way that can help people understand that. But simply put, any increase in pressure in your room is not wanted.

I think that’s a good safe statement to make and let’s face it when we design rooms, when I design a room, I want the frequency response to be +1 / +2 over a nice baseline. I don’t want any pressure variances and that’s of course my job as an engineer to achieve that and there’s various ways that we do that depending on room size and volume. But how do we get people to understand that that pressure increase means less of what they’re trying to accomplish?

AD: What will that actually sound like to people because you, as engineers, you guys are three experienced audio engineers. What does that actually sound like? How does that impact when you’re monitoring mixing?

Joseph Baffy (JB): If I can, if I’m catching on right, the example that I would like to bring to the table is let’s go with something that’s a little tangible to somebody who doesn’t really think in frequencies as much. Take the note ‘A’,and I’m using ‘A’ for a specific reason; be at 55 hertz, 110 hertz, 220 we also have a 176. Now a snare drum you know some of that lower “mmpf” in a snare drum is at around 178 / 170 hertz. So if I have, I’m understanding correctly, if I had a little bit too much pressure in which I had an overpressure around that 110 hertz or a 55 hertz or the 176, heck on 110, I’m not going to hear the kick drum quite right if I have an overpressure. Is that correct Dennis?

DF: Yes and haven’t we all heard recordings where we all say ‘Wow, he really got the drum right’ or ‘He really got the piano right’ or ‘He really got the bass right’. Well what did he do to get it right? He made sure that the room was out of the way and he was hearing everything in the recording.

So most of the time, I have a zillion recordings in there in my studio of pianos. Out of a hundred recordings maybe two or three sound good and what’s the reason for that? The reason for that is they didn’t take into consideration the room sound when they did the recording. That would be my best guess. Now there’s probably all kinds of other issues that we need to address but let’s just keep it simple and the reason that some recording sound good and others don’t is because the engineer that did the recording understood the marriage between the room and the microphone.

If you would like to learn more about room acoustics please sign up for my free videos and ebook by joining the mailing list here. I send room tuning tips and things for you to test in your room every Wednesday. They are easy to follow and really help you enjoy more of your music. And if you would like your room acoustic issues analysed for free by me then please fill in the form here and I will be happy to take a look for you.

Thanks and speak soon
Dennis