DCF - Digitally Controlled Filter (with manual Q)

The filter on the SQ-80 is a four pole analogue low pass filter - with manual "Q". The waves from DCOs are converted to analogue signals prior to entering the filter and then filtered. It is this true analogue filtering that gives the SQ-80 its old school analogue synth like sound. What is with this "Q" thing? "Q" is an electrical symbol meaning Resonance.
The filter can cut out the higher harmonics of a sound and make it sound smoother if the "Q" is low. With "Q" set high it will "emphasize" frequencies 'round the cutoff point, allow lower frequencies to pass, and cut off the upper ones. Using a "Saw" wave as a starter you can hear an of the wave; notice the slight edge to the sound. Notice how the sound it more muffed. Hear how the harmonics are almost picked out by the filter.
The controls along the top row are:

• FREQ: This sets the manual Filter Cutoff Frequency. FREQ ranges from 0 to 127 allowing control to about 1/4 step.
• RES(Q): This sets the filter resonance from none (0) to just under self oscillating(31). This filter will not self oscillate.
• KEYBD: This allows keyboard tracking. Set to the maximin value of 63 it tracks the cutoff frequency along with the note on the keyboard. If you want the filter to close down as you play higher just set this value lower than 63. The lowest value of KEYBD allowed is zero.

The next row has the modulators inputs. There are two pairs with two values each. For each modulator you can select the...

• Modulator type: Select on of the fifteen different modulation sources or off.
• Modulator depth: Sets the amount the modulation source will effect the filter cut off.

Need to filter to open wider as you play up the keyboard? Wait the maximum keyboard tracking ... tracks with the keyboard. No problem. Set one of the modulators to KYBD and the modulation amount to a positive number. Want an envelope to CLOSE the filter rather than open it. No Problem set the manual FREQ to a larger number. Set one of the modulator sources to ENV1, ENV2, or ENV3 and then set the modulation amount to a negative number.

---

Return to the SQ-80 main page
page created by: webmaster@dulcimoo.com
Changes last made on: FRI 22 OCT 2004
©2002-2004 dulcimoo.com, 1987-1989 Ensoniq (Now Creative Labs)