Basic Mixer Operation, Limiter, Equalizer Functions

BASIC MIXER OPERATION

1.Turn on the Power switch.

2.Adjust each channel level so that its Overload LED flick- ers only during very loud speech or noise.

3.Turn unused channel controls full counterclockwise.

4.Adjust the Low-Cut and High-Frequency controls adja- cent to each Input Gain control until all microphones sound alike.

5.Adjust the SCM800 Master level control for the desired output level, as indicated by the output peak meter.

6.Adjust the headphones volume level with the PHONES control knob.

LIMITER

The SCM800’s output limiter prevents distortion during loud program peaks without affecting normal program levels. In- creasing the individual or Master level controls will increase the average output and, in turn, the amount of limiting. The lim- iter prevents excessive overloading of devices connected to the SCM800 output. As supplied, the limiter is defeated.

The limiter threshold can be set for a peak output level of +4, +8, or +16 dBm. With the threshold set at +16 dBm, the mixer has 12 dB of headroom at a nominal level of +4 dBm. Refer to the Internal Modifications section for information on how to change the limiter’s settings.

EQUALIZER FUNCTIONS

Low Cut Filter (High-Pass)

The low-cut (or high-pass) filter allows all frequencies above its cutoff point to pass from filter input to filter output without at- tenuation, while frequencies below the cutoff are attenuated (see Figure 9). The cutoff point is defined as the frequency where the signal has dropped 3 dB relative to the flat, or band- pass, region. Below the cutoff point, the filter exhibits increas-

High-Frequency Shelving

The fixed-frequency equalizer produces a 6 dB boost or cut at 5 kHz and above (see Figure 10). High-frequency shelving is extremely useful for boosting flat frequency response, temper- ing very sibilant vocal microphones, or enhancing the sound of off-axis lavalier microphones.

ingly more attenuation as the frequency diminishes. The rate at which this attenuation occurs is defined in decibels per oc- tave (dB/oct). The SCM800 has a one-pole, low-cut (high- pass) filter of 6 dB per octave.

Low-cut filters are ideally used for attenuating, or rolling off, the audio signal where extraneous noise, excessive proximity ef- fect, or other unwanted material is present. For example, the low-frequency vibration cause by footsteps and vehicle traffic can be transmitted through microphone stands to the micro- phone, and then into the sound system. These frequencies, typically ranging from 5 to 80 Hz, are generally not desirable.

+2
0	FULL CW
0
-2

+10

0 -2

-4

-6 -8 -10

2001,000 FREQUENCY (Hz)

FULL

50%

ROTATE

FULL

CCW

10,000 20,000

-4
-4
-6
-6
-8			FULL CCW
	50%
	50%
-10	ROTATION


20	100	1,000		5,000
		FREQUENCY (Hz)

LOW–CUT FILTER EFFECTS

FIGURE 9

HIGH-FREQUENCY SHELVING EFFECTS

FIGURE 10