By Ray Rayburn
Ray shares a fix for a problem seen with Gain-Sharing Automixers in NION.
I helped develop the Gain Sharing automixers in Peavey’s Media Matrix product line when I worked for Peak Audio, and use them in many of my projects. They work great in the old MWare Frames, and in the XFrame88. Unfortunately as they come off the NION device menu, they don’t work correctly. Here is how to fix them.
NION Gain Sharing Automixer fixes:
- Drag a Custom Gain Sharing Automixer device into your project.
- Set the number of Channels you need in Channel Count.
- Select Highpass Filters on Inputs.
- Select Expanders on Inputs.
- If you need a non-automixed output as well as the automixer, un-select Filtered Link.
- Emulate the project so you can adjust controls.
- Open the device.
- Go into Edit mode.
- With cursor over top title bar of device window, right click and select Show Tabs.
- Open each and every High Pass filter device and change the Type from Linkwitz-Riley to Butterworth. We want the flattest response we can get in the passband coupled with the steepest roll-off below the cut off frequency. Butterworth filter type give us these characteristics.
- In one of the High Pass filters change the Frequency setting from 80 Hz to 125 Hz. Lower settings are only of advantage if the voice is an extremely low bass voice. 125 Hz gives us better low frequency noise rejection, but is not so high it can be heard on most voices.
- In one of the Expanders change the Threshold setting from 0 dB to -30 dB. This should be set to a level lower than soft voices. -30 dB seems to be a good setting in most applications.
- In one of the Expanders change the Ratio setting from 2 to 1.3. We want a very gentle expansion to aid in noise removal when no one is speaking on a given input. A Ratio of 1.3 sounds good.
- Open each and every Side Chain filter device and change the Type from Parametric to Bandpass. We are trying to select the frequency range we want the automixer to primarily respond to, which means we want a bandpass filter, not a parametric with the gain set to zero which does no filtering.
- Open each and every Side Chain filter device and change the Bandwidth from 1.00 to 2.00. We want a wide filter that passes the center of the speech band, but rejects low and high frequency noise.
- Open each and every Side Chain filter device and change the Frequency from 800 Hz to 750 Hz. Coupled with the other settings this selects the middle of the speech band.
- Open each and every Mean Square Detector device and copy out the Time Constant control and paste it into the main Schematic window.
- Select all the Time Constant controls you just copied out, right click and select Control Properties. Go to the Label tab and select None. Go to the Wiring tab and select Enable peer wiring node. Click on OK.
- Arrange all the Time Constant controls in a neat row and wire their nodes together. You will have one more more control than you have inputs.
- Open the Auto-mixer Gate device and change the Threshold from -90 dB to -60 dB. This Threshold is the level below which the automixer will ignore the inputs. Raising this setting helps the automixer ignore background noise. Settings higher than -50 dB should be avoided.
- Open the Auto-mixer Gate device and if the number of automixer inputs is 16 or less, change the Rest Gain from -21 dB to -12 dB. If the automixer has more than 16 inputs that will be active (un-muted) at the same time, then set the Rest Gain as follows: Rest Gain in dB = – ( 10 * Log (number of active automixer inputs))
- Re-emulate the project, and set one of the Time Constant controls to 50 ms. Since they are now wired together they will all go to this setting.
You will now have a correctly working Gain-Sharing automixer. Save your work!
Note: The Open indicators have absolutely no function and exist only because someone who knew such indicators from gated automixers insisted they had to be added. They light up when any given input has gain higher than the setting of the Open Threshold control in the Auto-mixer Gate device. That control, set by default to -9 dB, only effects the Open indicator light and has nothing to do with the actual operation of the Gain-Sharing automixer.
If you need assistance with your projects feel free to contact me.
Ray A. Rayburn – AES Fellow
K2 Audio, LLC
4900 Pearl East Circle Suite 201E
Boulder, CO 80301
303-865-5500 x 203