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Understanding and Calibrating Your System: An Understanding

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So your mix is done and everything is perfect. The drums hit hard, the guitars soar, and the singer sounds like an angel. But when you go to show the mix to the band on their system everything falls apart. The bottom end is missing, the mid range is cloudy, and the top end is ear piercing. What happened? Everything was perfect.


Also available in this series:

  1. Understanding and Calibrating Your System: An Understanding
  2. Understanding and Calibrating Your System: Monitor Speakers
  3. Understanding and Calibrating Your System: Amplifiers
  4. Understanding and Calibrating Your System: Convertors

Maybe their system was just EQed really oddly? Or maybe it was your system that was way off.

In this tutorial series we are going to look at what makes a properly calibrated system and how to achieve the best results possible at home. Everything from basic acoustics, to speakers, to reference levels will be discussed. So if you are ready to get your system up to snuff then jump in and get ready to be calibrated!


A Quick Word on Acoustics

First and foremost the acoustics of your room will play a bigger role in how your mixes sound than anything else in your system. A room with poor acoustics will require you to over compensate on your mix and will give you an extremely inaccurate mix when you take it to a friend's house or even in your car.

That being said, most of us do not have the money required to properly build a room specifically to avoid these problems. However there are a few easy fixes for some issues and other ways we can safely compensate for these problems.

Before you go crazy with the sound foam lets make one thing clear; sound foam does not isolate your room from outside noises, and vice versa! Sound foam when used properly will help stop reflections in your room, but does not have the mass and acoustical properties to effectively isolate your room.

With that in mind lets look at some common problems acoustically with our rooms.


Flutter Echo

This acoustical issue is when you have a distinct tight echo in your room that can muddy your room and cause all sorts of problems in your mix. To tell if you have flutter echo problems simply clap very loudly and listen for a delay type of effect coming from the walls.

To fix this sort of problem either hang sound foam or towels or blankets on the walls to eliminate the flutter echo.

Remember, sound foam or any other absorbing material does not isolate sound; it simply stops reflections! However if you have a low frequency flutter from say kick drum type of sounds, you will need a denser material to absorb those frequencies.

Room Modes

Most of us are not blessed with an irregular room that does not produce any resonances, and as such we must contend with the room modes of square and rectangular rooms.

Essentially, room modes cause certain frequencies to be accentuated (or reduced) and can cause us to under mix these frequencies since they already sound loud from being amplified by the room. While the math for these equations can start simple, the more complicated the room shape and type of mode (axial, tangent, and oblique), the more complicated the math gets.

Instead of you trying to manually perform these calculations, I recommend using an online room mode calculator to determine what the peaks and valleys of your room are; this will get you in the ballpark. This will then allow you to fine tune your absorptive materials so that they work on your most troublesome frequencies. No need to absorb 100 Hz when your problem is at 70 Hz!

Dead or Alive

Another common issue that we also must acoustically tend to is whether to mix in a live room or a dead room. The more absorptive material we place in the room, the more the room will lack reflections, which then creates the dead room sound.

While a dead room is arguably the most accurate type of room, it is not a very natural mixing environment; your mix will probably never be played in an anechoic chamber!

You do not want tons of reflections bouncing around everywhere, but they are necessary to some degree in order for us to get a good sense of how the mix may sound in a typical environment. I therefore recommend going for a controlled room that has no audible reflections and gets rid of the nasty ones, but still allows the room to 'breathe' a little.


What Makes a Good System?

Before we can really start to optimize a system we first need to decide what pieces go into the system. Furthermore we to make sure we do not have any unnecessary components either that could end up making our system muddy.

For any audio engineer, having an accurate system is more important than anything else. Having that extra bass like in your car or having a really bright set of live speakers that cuts through a crowd does not have a place in a critical listening environment.

When mixing we cannot assume that our mix will not be played somewhere or not on these particular speakers, or only on these ear buds, etc. Because of this, we need our system to be very middle of the road so to speak; accurate and truthful sounding.

When you mix on a bass heavy system you will end up sounding weak in the bass region on a normal system. If you mix on a system with a dull top end you will end up sounding overly bright on a normal system.

So with that all in mind lets take a look at what goes into a good system.

Speakers

The last part of the chain and arguably the most important. A set of speakers can either make or break the chain in your system. It is the last link (electrically anyways) in your system before it reaches your ears.

A true quality set of reference speakers will reach from 20 Hz all the way to 22 kHz and beyond and keep the frequency ruler flat. More often than not, these types of speakers are very large and have at least a 10 inch woofer if not a 12 inch for the bottom end, one or two 8 inch or 6 inch woofers for the mid range, and a tweeter for the top end.

Of course the simple single woofer and tweeter monitors we see in studios all around the world are still valid, but not all of these monitors translate up to hi fi systems as well as they translate down to consumer grade speakers.


Power Amplifier

While the speakers may be the most important, they are of no good to you if you do not have an power amplifier to give them some juice.

Some speakers will have an integrated power amplifier that are designed to match your speakers; these are known as powered speakers. On the other end of things you will have power amplifiers that power passive speakers which do not have an integrated power amp.

While in an ideal world a power amplifier would simply just give us more power and not alter our signal, this is not always the case. Just like with speakers, an amplifier has its own frequency response which can affect the tone of your system. It is because of this why you simply cannot use any amplifier that meets the wattage and impedance ratings of your speakers. While amp A and B may both be 300 watts at 8 ohms, B may sound more linear and accurate while A may have a bigger bottom end and top end for say live sound use.

Keep in mind also the different classes of amplifiers; namely A and AB for audio. A class A amp is generally considered the most accurate due to the fact that, in very basic terms, it is always running. Because it is always on (when powered on of course) it can reproduce transients exceptionally well and handle a wide frequency range. However because it is always on it produces massive amounts of heat and is very heavy (the weight comes from its simple circuit that requires large parts).

Class AB on the other hand is in a constant switching state that conserves power and therefore heat and can be made much smaller and cheaper. However due to its switching nature it is prone to producing distortion if not designed carefully.

Some argue that only a Class A is truly accurate while others assert that Class AB amps have come so far in design that there the two are audibly indistinguishable.


Convertors

The last piece to the puzzle is actually the beginning of our system once it leaves the computer, the Digital to Analog converters. Having a quality amp and speaker will mean nothing if your high definition audio inside your computer is turned analog by a second rate convertor.

Often times you will see professional studios and mastering houses with a whole separate set of converters strictly for the output stage from the computer to the amplifier. Why? Because these high end boutique converters are very accurate.

That is not to say however that a $500 audio interface's convertors are bad, they are still accurate; just not quite to the degree of very high-end converters.


Now some of you will have noticed that I have neglected to mention other possible pieces of gear such as EQs, crossovers, etc. The reason for this is because they are not directly necessary for a good system.

Remember, the more pieces you add the better chance you have of degrading the system. Now that is not to say you cannot use these pieces to help your system along, but you really should not depend on them if you can at all help it.


Getting to Calibration

Calibrating a system is not as hard as some may make it out to be. Some tweaks are electrical while others are acoustical. Let's first start out by doing some basic setup that will get us close to our desired calibrations and then move onto some fine tuned tweaks.

  • Start out by deciding where exactly you wish to sit in your room. You will need to base your entire setup around this position. Ideally you will want to leave enough room so that your speakers are away from the back wall and as far away from the corners are possible. This will help prevent any unnecessary bass build up that will skew the sound spectrum.

    Additionally, you will want your sitting position to be as far away from the back wall as possible; so make sure you position speakers so they aim long-ways in the room.

    One trick to getting a good sitting position is to use the 38 percent rule, which states that the most ideal listening position is 38% of the length of the room. So if the longest part of your room were 12ft, then your ideal sitting position would be 4.56 feet back from the wall you are facing. Keep in mind this is only theoretical and only really works with rectangular rooms, but it is always a good fail safe to start from.

  • With your sitting position decided upon you can begin to place your speakers. The tweeter portion of the speaker should be roughly ear height and the angle of the speakers should be about 45 degrees facing inward towards your ears. What this does is creates a nice even triangle with your ears as one point and the cones of the speakers as the other two.

    If your speakers have offset cones and tweeters where they are not perfectly down the middle, or you need to lie your monitors sideways (ala NS-10) then be sure to approximate the middle of the speaker as your reference point for the angle.


  • Next connect your converter to your power amp and the power amp to your speakers. You should have a line level analog signal going to your power amp so make sure it is not somehow mic level or digital by some mistake.

    With everything up and connected we need to now set our gain appropriately so we do not created any unneeded hiss.

    First start by insuring that you are sending maximum signal from the convertor to the power amp but do not turn the power amp itself on or you may blow the speakers! Make sure you double check all volume gains inside your computer that may affect the audio output such as specific software for the converter, windows or mac audio, etc. Next create yourself a pink noise sample at -20 dBfs (-20 in your DAW) to play through the speakers; this will be our volume calibration reference.

    Next you will need a sound pressure level meter to measure the volume intensity of your system. Oddly enough, the SPL meter from Radio Shack is an industry standard so if you can, use that model!

    Make sure your sound pressure meter is set to C weighting, the range is set to 80 dB, and that you are holding it at your chest. Double check to see if your power amp has a gain knob or not, if it does then turn it all the way down, loop the pink noise, and slowly bring up the gain on the power amp until your sound pressure meter reads 83 dBSPL.

    If your power amp does not have a gain knob, then turn the output of your converter all the way down and slowly bring that up until your meter reads 83dpSPL. After you have your 83 dBSPL proceed to mark that level on your gain knob with a piece of electrical tape or some other mechanism.


  • With our reference level now set you can begin to add sound foam, diffusion, etc. as you need it. Assuming a rectangular room, I recommend adding absorption on the ceiling just in front of where you are sitting, and adding some to the side walls just in front of where you are sitting.

    In addition, if you are on a hardwood floor I would recommend adding a carpet underneath the ceiling foam. The reason for these placements is to help minimize early reflections which cause the most issues with the acoustic properties of the room.


Working With the System

So now that we have our system set up how can we effectively use it? For starters you should have a better sound simply by having the speakers in an optimal placement. If you added any sound absorption material, even better!

But what about that reference level of 83 dBSPL? Well this is considered by many to be the magical listening level that produces an accurate frequency response in the human ear that can still be listened to for a reasonable duration before incurring any hearing damage.

However remember how I told you to mark that level on your gain knob? The reason being is while you could theoretically mix at this level for a few hours, some may consider this an unsafe level for general mixing. Instead turn down the reference level to approximately 75 dBSPL for basic editing and mixing and turn up the reference level to the 83 dBSPL for critical listening when you really need to hear the tiny details. This way you can really get a good mix and preserve your hearing!

Now what if you feel your system is still lacking in say the bottom end or maybe is too dull? Well you can add an equalizer to the mix between the convertor and the amp but do be careful! There will come a point in which you simply are going to not be able to compensate electrically or acoustically for the shortcomings in your system.

The only way to overcome these shortcomings is to adapt to them. Listen to your favorite songs and albums on your now calibrated system and really learn what they sound like on your system. In addition, try your very hardest to listen to at least CD quality tracks, no MP3s or YouTube!

Sure the bass may not be as loud on your system, but if your mixes match the recording then you know your mixes should be OK. Eventually you will learn your system and you will not need to be constantly aware of any pitfalls. Often times engineers will say you need to listen through a speaker; this is what they mean.


Final Thoughts

So where do we stand now? You have a better grasp on what goes into a good system, how to set yours up, and how to keep the acoustical limitations of your system and room in mind so you can mix appropriately.

In the next part of the series we are going to look at bass management and general speaker design so we can get a better feel for possible upgrades to your system and how to handle specific pieces of equipment better.

That is all for now folks, thanks for reading!

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