The Mechanics of Mixing

 First we need to talk about a few rules.

 I.          To achieve a proper mix, all sources (vocal, instruments, drums, etc) should be heard equally except in the case of rule number two.   

 II.         The lead source (vocal, instruments, drums, etc) should be turned up twice as loud as the other sources.

 There are a few physical rules that need to be learned.

 A.        Sound volume is measured in decibels (db).   Decibels are a relative measurement.  In other words, I might say my sound system is 10  decibels louder than your sound system.   

B.         It takes 10 times the power to be twice as loud. 

C.        A sound that is twice as loud is said to be 10db louder.

D.        Therefore, a volume increase of 10db represents a doubling of the volume and a 10 times increase in power.  A volume decrease of 10db represents a halving of the volume and 1/10 the power.

E.       60db of dynamic range is the achievable goal of any quality sound system.

This brings us to this realization.  For a 10,000 watt speaker system to have a 60db dynamic range, the power will have a range from .01 watts to 10,000 watts.  The chart below explains this reality.  

This brings us to another realization:  Noise reduces a sound system’s dynamic range.  If you have 1 watt of noise and a 10,000 watt sound system then you only have 40db of dynamic range.  You would have to increase your sound system’s power to 1,000,000 watts to achieve that 60db of dynamic range again.   See the chart below.  

For most people, it is impossible to purchase 1,000,000 watts.  Therefore, if you have any intentions of achieving 60db of dynamic range with your sound system, you must keep the background noise to a minimum.

Now back to mixing.  On most mixing consoles, you will find that every channel has a button, a knob and a meter that work together.  They are the “gain control” located at the top of each channel, the “PFL” or “Solo” button and its associated meter.  With the channel slider turned down, press the PFL button on the first channel.  Have your source (vocal, instruments, drums, etc) for that channel sing or play and bring the gain control up until its associated meter shows a reading of 0db.  Most “VU” meters are labeled at -20, -10, 0, +1, +2, and +3db and above.  The red line is at 0.  If you are fortunate enough to have a large mixing console with a meter on each channel then you won’t have to PFL the channel.   Just bring the gain up until each channel’s VU meter reaches the red line or 0db.   By doing this for each channel, you are making the volume at the channel slider equal for all channels.   Therefore, to follow Rule #1 you would put all the channel sliders at the same place.  That way everything is equal.   The only exception is the “lead” which is turned up 10db so that it is heard over everyone else.  The “lead” is the part you hum to when the music is playing.  Now the question is where to set the channel sliders.  Let’s look at this.

If you put a source in channel one and set the gain as was discussed above and then route that channel to the main output slider and set it and the channel slider to 0db then you will find that the main meter on the mixer will read 0db.  In other words, each channel, when set properly, can bring the entire mixer to full volume.  If you add a second channel, then the main meter will read +6db and you will need to bring both channels down -3db so that the main meter is back down to 0db.  When you add a third channel again the main meter would read +6db and the third channel would have to be reduced by -3db to match 1 & 2 and then the three channels would have to be reduced by -1db each to bring the main meter back to 0db again.  As you add channels the total reduction approaches –6db on every channel but never actually reaches it.  In calculus they call that the limit of the equation.  Therefore, the place to put all your channel sliders is around -6db.  Because they only mark the -5db and -10db point on the channel slider it is easier to set all your channel sliders at -5db. Then to set the “lead” channel you need to raise that channel slider to +5db which is 10db louder.  If the lead changes, (vocal to guitar solo for example) the lead (vocal) that is finished needs to be lowered -10db which brings it down to the line again and the new lead (guitar soloist) needs to be raised up 10db.

I had a job one time with multiple stages.  I had my nine year old son with me and after I had set the system up and the band started playing I was called to another stage to help with a problem.  I told my son to keep the line in tack and turn up and down the channel volumes just like I described above.   Then I left.  I came back 30 minutes later.  The band was on break and so I went to the band leader (actually it was a community orchestra of about 20 people) to see how things went and he told me it was the best mix he had ever had.  He didn’t know a nine year old mixing.  My son just followed orders and mixed mechanically.  He didn’t mix with his ears and he didn’t mix with his feelings.  He just mix mechanically like I taught him on the spot and it was the best mix that band ever had.

This is the basic mechanics of mixing and you will find that on a moderate to large sound system this works flawlessly.  The only problem is most people don’t get to mix on real large sound systems and so the sound from stage has to be taken into consideration.  Basically you have two ways to handle this problem.  One way is to use the sub masters to group common instruments together.  For example you might use sub master one for vocals, sub master two for instruments and sub master three for drums.  That way you can turn the instruments and drums down a little at the sub master to compensate for their stage volumes.  If you don’t have sub masters I suggest using your channel gain controls to turn the instruments and drums down so as to maintain your straight line on the channel sliders.  The professional sound person always maintains that straight line on the channel sliders and makes adjustments at the channel “gain” control or at the sub masters.

 Some music has accented bass guitar and kick drum.  If you want to accent these or other instruments you can send then to two sub masters for added volume.  The increase is 6db to be louder to be precise.  For example, I usually use sub master four for this purpose.

 The advantages of using proper mixing techniques are:

 1.         Volume controls that are set alike are alike in volume.

2.         Driving the front end of a channel to its maximum usable volume keeps the signal to noise ratio the best it can be.

3.         Setting your line at the proper level assures you will get full power, but won’t over drive the mixer.

4.         A great mix.

The math proving the -6db point for sliders.  (This is for the math freaks)

By William Mellon

PS:  To be continued.