Thursday, August 14, 2014

EQ Part 2 (of 3 maybe?) - EQ a room and the importance of objectivity

So last time I posted here, I laid out the foundations of EQ...  well some of them anyway.
But like all good things that we know of in the audio world, the effect was created for one reason, and then it was utilized in a possibly unexpected way to create a useful tool to anybody mixing audio.

One way it became useful was to EQ physical spaces...
Walk with me down storybook boulevard, and let's examine a possible reason to EQ a physical space.
You are a concert touring musician (or really anybody who is setting up a loud speaker system), and your system was set up in an arena in Las Vegas...  Your next stop is in a much smaller arena in Reno.  Your system is set up the same as it was in Las Vegas, but it just simply sounds different than it did in Las Vegas...  What's the difference between these two cases.  The biggest difference is the room itself.  IF you as the sound guy did your job correctly, and made the frequency response in the Las Vegas room the way it is supposed to be*, then that same setting applied to the smaller arena in Reno will likely yield you different results.

Why is that?

It could be due to many many factors including but not limited to height of the deck above the floor, slope of the deck (assuming the floor is level), building material differentials such as painted concrete vs wood.  If there is ice under the floor of the arena, what materials are used to cover the ice?  The physical VOLUME of the building will affect the sonic characteristics of the sound system being set up in the building (axial, tangental, and oblique modes all get affected)...   The end result is that there are TONS of reasons that certain frequencies will be reinforced, while other frequencies experience destructive interference.

I just mentioned a big word there...  Frequency.  If we know frequencies are being affected, just like the olde skoole example of the phones (see EQ part 1), we can EQ it back to perfection..

In many cases this can be done automatically with the right equipment, but let's assume we're new at this and need to figure it out the old fashioned way.  You could go train your ears for a long time (or purchase David Moulton's Golden Ears system, which is highly recommended by me, and can be read about here: ) - then try to do it by ear alone, or you can use an RTA (real time analyzer) in conjunction with a calibrated test measurement microphone, and a pink noise generator.

Pink noise, which is white noise with a particular EQ filter on it already, is played through your system. This pink noise has a known frequency response.  When this pink noise is heard via a calibrated test measurement microphone, and then connected to an RTA, you can see exactly what frequencies are reinforced, and what frequencies are destructively interfered with.  You can then connect up a Graphic EQ to the system, and simply turn up and down the appropriate frequencies to get your room to sound like it is supposed to*.

Because you are all sharp as tacks, and have noticed a couple of nifty little "*" marks...  I put those in because what the room is "supposed to sound like" is a very subjective thing...

Many of you who might read this would also suggest like me that of course the room is supposed to have a flat frequency response, which is to say that no frequency ranges are louder or softer than others within a realistically wide band... for instance, you would be flat from 32 Hz to 15kHz...

I realize that 20Hz to 20kHz is the model hearing range, but in reality, try to find 15k in an MP3 or on the radio, or YouTube, or any other popular streaming audio and I would be shocked if you had speakers that could accurately reproduce it (Beats won't do it), or if it even existed to begin with.  I will launch into the tirade of dumbing down of our society's ears in a later post.

Consider the source material...
I would bet that in most dance or hip hop or rap or anything other than classical styled music, flat is NOT the way to go...  That realistically if you aren't knocking peoples stomachs into their throats with too much bass, you aren't doing it right (at least at the arena scale).  If you are in a church you will likely want flat, but consider Jay Z...  Do you really think Jay Z wants flat at one of his shows?   How about Usher?  How about Beyonce?  How about Matt Azevedo?  Wait, who's that guy?  Check him out here...  

the point is simply that whenever we talk audio in the real world, things are VERY SUBJECTIVE...  so when I say things are the way they are supposed to be, it is intended not as a specific how it is supposed to be universally, but more how it fits best for the moment for the application.

All EQ is subjective in nature, because each of our ears hears things differently.
There is a good book out there that delves into the physical versus artistic applications of how we hear sound.  It is written by a gentleman named Dr. William Moylan.  It is called The art of recording: understanding and crafting the mix.  If you are interested you can find it here:
In this book it delves into the idea that it is not enough to say something sounds tinny or something sounds bright, but we need to move beyond this type of vocabulary into something realistic...  So we could say that there is too much of 9kHz-11kHz, as opposed to "this is tinny", or "this needs to be fattened up".  The statement this is tinny is subjective.  What I think of as tinny and what you think of as tinny might be completely different.  You think tinny as too much higher frequency information... I think of it as not enough low frequency information...  so you can see how these subjective terms can be destructive to the creative process.  If you say "turn down 14kHz by 3dB", I can take that and actually do something about it.

The is a LOT to be said about the importance of moving away from subjective audio terms, and into objective audio terms, or physical audio terms.

EQ is one of the places where this will play the most...  An RTA doesn't tell us that the room is tinny, no it says what the real frequency response actually is so we can actually do something about it.  This is something everybody who likes audio should consider as you journey through the audio world.

I have to apologize, because I thought I could get this into 2 parts, but then this part would have been exceptionally long (not that it isn't anyway).  So join me again for Part 3 of EQ, where I deep dive into the Studio parts of what we can do with EQ's...  Not only what we can do with EQ's but also what we are ACTUALLY DOING when we do stuff with EQ's...

Let me know your horror stories of Frequency stuff in the concert environment, and how you overcame them with EQ....

Thanks for reading

No comments:

Post a Comment