RSS Feed

Recording Mythology, Pt. 5 / Frequency Equalisation

 

I think that one of the most misunderstood and often overlooked factors in obtaining good sound recordings is the artists consideration of the entire audio spectrum, the impact that creative use of EQing and the application of room treatment has on the process and how the judicious use of shelving is useful in order to enhance the finished product.

The thing for the home recording artist to bear in mind is the fundamental differences between the ear and the microphone. We use our ears so much of the time that we are unaware that what we hear is constantly undergoing a mechanical selective analysis. That is to say that our brain takes a great deal of what ours ears hear and disregards it because it is either annoying and/or useless audio information. A certain amount of conscious selectivity may be applied from time to time, such as concentrating on a particular voice in a crowded bar, but our brain filters a great deal of noise out without our conscious participation. Microphones have no such way to filter out such noise. They pick up everything. Another difference that we need to be aware of is that most microphones are sensitive to frequencies far beyond those of our ears and that a decent mic generally ‘hears’ all of these frequencies in a very linear fashion, called flat response. This property, which is a necessity, also has its drawbacks.

For instance, all of us, at one time or another, have placed a mic on the table in front of us, hit the ‘record’ button, and started strumming and singing. Afterwards, upon playback, we were shocked at how awful it all sounded. ‘What is all of that damned racket?’ we probably wondered. In effect we recorded not only the instrument and the vocal, we recorded early reflections (compliments of the table top), hard wall room reverberation, as well as the ‘quiet’ roar of the central air unit. In other words, all of the echos which bounced off of the walls of our den or bedroom eventually found their way back to the mic diaphragm. The sounds that our brain ignored. One thing is certain, we can’t ignore them once we hit the playback button. What to do? There are three things, or any combination of two: EQing, compression and/or the application of acoustic treatment to the walls and ceiling.

EQing, or equalising, is used in respect to the shaping of sound, or the manipulation of the frequency curve. ‘Flat response’ is a term we see tossed around all of the time and seems to be a major factor in the promoting and subsequent selling of microphones, monitors and other related items, along with the highly touted frequency response. Most often these specifications will be related in hertz, which is a fancy word for cycles, which is really just another word for the length of the waveform of any particular frequency. (Sound science gets rather deep.) It will be specified that a particular microphone or monitor has a frequency response of 20 hertz up to 20 thousand hertz, or kilohertz, and that these frequencies will be reproduced flat. That means that a particular frequency will be represented at the same volume as any other given frequency. Lots of people will pour untold amounts of money into the purchase of both items based on these qualities alone, but consider this: The practical range of our hearing is more along the lines of 60 hertz to around 14 kilohertz, and our ears are not flat. On top of this, the range of most music is from 41 hertz (low E on a bass guitar) to somewhere around 12,500 hertz (cymbal crashes). Not only that; most ‘noise’ falls dead in the middle of the musical spectrum as well as our hearing. To complicate matters, our ears exhibit an anomoly known as perceived loudness, in which a a given tone at a set volume, or amplitude, sounds louder or softer than that of another given tone. Back in 1933, a couple of fellows at Bell Laboratories arrived at a graph to plot these perceived differences:

 Image

The broken blue lines in the graph  are known as the Fletcher-Munson Equal Loudness Contours, which was named after the two gentlemen who conceived it. The red lines, arrived at later in the 1960s, are referred to as the ISO 226 Contours; fully revised. Most old sound engineers still insist that the old F.M. contours are closer to what our ears actually hear. 

With this in mind, we really start to ask ourselves, “Why do I need such great monitors and microphones if my ears suck so badly?” Of course there are valid arguments to be made concerning the frequency response and curve of these pieces of equipment, but the bottom line is that they aren’t going to save you from creating a bad mix, and they aren’t going to make you sound better than you really do. As a matter of fact, they’ll probably make your work wind up sounding worse, since they are so unforgivingly accurate.  And this is precisely why we want these tools. Our goal is to raise the apparent loundness of certain frequencies while lowering that of others in order to make all recorded tracks audible.

But we have to start somewhere. 

Once again, the best advice that I can give an artist who is interested in home recording is to buy decent, mid-grade equipment and not get all caught up in the numbers games. If an item fits into your budget, do an Internet search on the item and find some user reviews. Decide what you want, and buy it. And don’t buy an item based solely on the brand name of the manufacturer. Likewise, don’t avoid an item based on the brand. When I started out, all that I could afford was Behringer and Peavy equipment. And I got all of my gear on sale or clearance. But I wasn’t looking to impress anyone with my studio setup, I was looking to get my stuff recorded. I am willing to announce that my older MXL 960T large diaphragm tube mic still plays a prominent role in my recordings and that it sounds fine for what I do. (I did however, change out the cheap Chinese 12AT7 tube with a 12AU7 Groovetube). I will also admit without hesitation that the Behringer Composer Pro is one flexible compressor, albeit the learning curve was a major pain in the ass (as is with most compression equipment) and the ‘automatic’ presets were useless.

Treatment is somewhat expensive if you are going to do it right, and there is alot to learn about acoustics if this route is taken. This type of absorptive attenuation can tame an overactive room down, on the other hand. Every room has two or three resonant frequencies and several more harmonics. The treatment is a great way to go, but the commercially available stuff requires using adhesive to apply it to the walls. Do you have a mom, landlord or wife who is going to raise hell? Maybe you’re already surviving on macaroni and cheese and can’t justify the cost. Then get resourceful. To start out with, I used padded moving blankets which I tacked to 1″ x 2″ wooden strips cut to length, and hung from the ceiling with hooks and eyelet screws. They proved surprisingly sound absorbent. The trick was to break up the sound waves, so I suspended them in the middle of the room, all at weird angles, instead of against the walls. Sure it looked goofy and I had to maneuver around them, but they accomplished the task..at ten bucks each.

If you are recording using computer software, or a DAW with effects included, the EQ and gating features are designed precisely to deal with such noise issues. If your device or mixer  doesn’t include these extras but comes with either insert jacks or effects send and return jacks on the back of the unit, you have another option. It is a simple enough procedure to run two cables out of any two channels of your DAW or mixer into any compatable ‘outboard’ unit and back out into the DAW. This can be done with a dual channel 31 band graphic EQ. It is my experience that most consumer DAWs have inadequate EQs built into them, generally consisting of either seven or nine frequency bands. With these built in units, the Q or frequency spread is too broad to be of much use, as an adjustment of one band will also effect adjacent frequencies.

With a 31 band unit, it becomes easy to notch problem frequencies that you may be experiencing as well as removing much of the extraneous resonance. The purpose of the EQ is to cut all frequencies that we find distasteful or distracting, while serving to boost those which we may find lacking. Whereas this is a highly selective and subjective process, common sense tells us, for instance, that we may easily cut all of the frequencies outside the range of our acoustic guitar, as well as reduce much of the “boominess” that is often experienced. It is surprising how much cleaner a recorded acoustic guitar will sound if all frequencies below 200 hertz are cut or “rolled off”. Sometimes there is a problem frequency around 1500 hertz that can be easily contoured using an EQ. Remember that nothing you do will take the place of learning to properly use the gear and apply the effect judiciously, all the while remembering not only to listen, but to hear.

In order to learn how to use an EQ properly, we must also train our ear to recognise approximate frequencies. This is another area that requires more time and training. Several companies manufacture tone CDs for calibrating analogue equipment and testing the response of audio speakers  These CDs are also very good at testing one’s hearing! 

More on the use of compression and gating next time!

Johnny is a songwriter and composer who is very detail driven and extremely hard to get along with.

Advertisements

About Johnny Nowhere

Johnny Nowhere is a songwriter/composer and owner of Hell Paving Company, music publisher. Johnny doesn't really exist outside of the music industry and Facebook. He is simply a figment of my imagination.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: