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All information in these pages is copyright (c) 1989-2003 by Roger Nichols. All rights reserved. Permission for personal reference only, and may not be reproduced by any method without written permission.

The Industrial Resolution

By Roger Nichols

Mouse vs. Fader

For some reason it is hard to control delicate computer functions with a mouse. The mouse is fine for pointing and clicking, but when the task at hand requires fine continuous movements, the mouse just rolls over and plays dead. Have you ever tried drawing a picture on your computer screen with a mouse? The pointer jumps because of the inaccurate roller ball interface, and the scale of what you see on the screen does not easily translate to the amount you are moving the mouse, especially when you run out of mouse pad and have to pick up the mouse and move it in the middle of a stroke. This is why artists and designers use tablets to input drawings into the computer. The movement of the hand and stylus are more natural and are easier to translate into computer vectors.

The same thing happens when trying to mix audio with a mouse. You click on a screen fader and move the mouse. If you move the mouse one inch forward the fader moves some amount on the screen. Because of mouse stutter, if you move the mouse back the exact same inch, the fader on the screen will not be back exactly where it was when you started. A physical fader that you can move up and down is much easier to use for riding vocals and other gain varying instruments. When I want to ride something up and then bring it exactly back to where it was, I place my finger below the knob as a stop. I can ride the fader up, and then snap it back to my finger and the level drops back to exactly where I want it to be. You just can’t do that with a mouse.

Now that we have determined that nothing is better than a real fader, we should talk about the resolution of the real fader. It has already been determined that 100mm is a good length for a straight-line fader. If you lean your forearm on the armrest at the front of the console, the range of movement in your wrist is comfortably 100mm. You can move the fader from the full off position to the loudest position without lifting your arm from the armrest. The highest resolution available in the fader movement is at the point where the wrist is relaxed. At this point you also have the most amount of control over small movements in your wrist.

When console automation came on the scene in the early 70s with the Allison 56k the range of fader movement had to be quantified into discreet steps that could be detected and reproduced by the automation computer. After subsequent generations of console automation, and input from scores of automation users, a value was reached of 1024 steps to represent the position of an analog fader. At the "sweet spot" (about 25% down from full fader level) one step in the fader movement corresponded to 0.1dB of gain change.

One dB is defined as the smallest amount of change in level detectable by the human ear. This is based on the level change of the entire sound that is being heard, If you change the level of the mix, or the level of a soloed vocal, this definition holds true. If, however, you have a reference to compare the level with, then a 0.1 dB change in level is readily apparent. If you are comparing the input to the output of a DAT machine, you can easily tell if the levels are 0.1 dB different. If you are listening to relative balances in a horn section it is easy to hear the difference when one horn is turned up 0.1 dB.

One more factor comes in to play with audio faders. It is the logarithmic taper of the audio fader. As the fader is pulled down toward the off position the amount of attenuation increases rapidly for the same amount of movement of the fader. A half-inch movement at the top of the fader is approximately 5 dB. At the bottom third of the movement the attenuation is 20 dB. The next half-inch is 50 dB.

If you recorded the vocal much louder than all of the other instruments, then the fader position will be much lower in the final mix situation. Because of the taper of the fader, small physical moves will translate into larger changes in level. If the moves are automated, the steps will be 0.2 dB or greater on our 1024 step faders. If this happens, use the line trim to lower the level of the vocal so that the fader can be moved up into the "sweet spot" of the fader, or up near the top 25% of the travel. The sweet spot is usually marked as zero on the fader. Levels above this reference will be marked as +5 and +10 while markings below this level will be —5, -10, -20, and -40, down to infinity. Any fader movements in this area take advantage of the smaller 0.1 dB steps and make riding the vocal much more accurate.

Small format digital consoles use larger steps for automation data. The typical value is 512 steps. This means that at the most sensitive fader position the smallest step will be about 0.2 dB. As you move the fader down the steps quickly change to 0.4 dB then 0.8 dB and 1.2 dB. You can quickly realize the benefits of 1024 step faders.

Pro Tools uses 0.1 dB steps for automation, and so do most of the DAW type systems. It is actually easier in a DAW because you are just dealing with computer information and can choose any step value you want. The value just becomes a multiply value stuffed into a DSP to get the levels you want. The Pro Control and the HUI provide the same resolution of control.

If you must mix by using the mouse, here is a tip. Most people set the mouse sensitivity so that the mouse pointer moves a lot with a small physical movement of the mouse. If you try mousing a fader you will see big jumps in the level corresponding to the coarseness of the mouse setting. If you set the mouse to the slowest response you can more easily control the fine movements of the fader in 0.1 dB steps

Fader Quality

The high quality automated Penny & Giles faders used in large format consoles cost about $1000 each. They have very smooth and silent audio qualities and are touch sensitive. I mean "really" touch sensitive. The conductive fader knobs are electrically connected to a circuit that detects the change in capacity caused by the touch of a finger. Without moving the fader, an LED will light when the fader is touched.

Part of the cost of the fader is the accuracy of the resistive element that passes audio in an analog console. Digital consoles do not pass audio through the fader, so this element can be removed. No signal actually passes through the fader in a digital console. There is only a motor to move the fader and a resistive ladder that sends the current position of the fader to the automation. The level of the audio is changed in the DSP. It doesn’t really matter whether it is a physical fader or a picture of a fader on a screen.

Small format digital consoles use a different method for touch sensitivity, which allows for very inexpensive faders. The automation continuously looks at the position sent by the fader. If the position of the fader is different than where the automation set the fader, then it must have been moved. Notice I said "moved". The fader must be moved. The automation does not actually sense that the fader was touched. The fader movement sensing is usually set to trigger if the fader was moved two fader increments to avoid false movement indications. This means that if you are going to make a small ride in a vocal track, you must move the fader by two steps (0.4 dB in the sweet spot) before the automation knows about the move. This means that the initial movement will be late (it won’t be detected until you have already been moving the fader for awhile) and the change in level may be larger than you want it to be. I always try to move the fader in a hole between lines of the vocal to get the automations attention so that automation data is being written before the spot that I actually want to ride.

Now you know everything about console faders. Next month we will cover the Neutron capture cross sections of trans-Uranium elements and why the increments are measured in Barns.