Instruction Manual

ManualsBrandsDoepfer ManualsAudioA-121 12dB Multimode VCF

doepfer

System A - 100

VCF 2

A-121

1. Introduction

Module A-121 (VCF 2) is a voltage-controlled multi-

mode filter with a cut-off slope of -12 dB / octave.

Four simultaneous outputs are available, each with

different characteristics: low-pass, band-pass, high-

pass and notch (or band reject).

The cut-off frequency determines the point at which

the respective filter effects appear. The frequency can

be adjusted manually, or by voltage control (Filter

modulation, for instance by an LFO or ADSR). Two

CV inputs are available, whose control voltages are

summed.

Resonance (Emphasis or Q ) can be adjusted

manually, or by voltage control (voltage-controlled

resonance / VCQ), right up to self-oscillation, in which

case it will behave like a sine wave oscillator.

Audio

FCV 2

QCV 1

QCV 2

Res.

FCV 1

A-121

MULTIMODE

FILTER

Freq.

Audio Level

Low Band High Notch

Summary of content (10 pages)

PAGE 1
System A - 100 doepfer VCF 2 A-121 1. Introduction Audio Level Audio In A-121 MULTIMODE FILTER FCV 1 FCV 2 FCV 2 Freq. QCV 1 Res. QCV 2 QCV 2 Low Module A-121 (VCF 2) is a voltage-controlled multimode filter with a cut-off slope of -12 dB / octave. Four simultaneous outputs are available, each with different characteristics: low-pass, band-pass, highpass and notch (or band reject). The cut-off frequency determines the point at which the respective filter effects appear.
PAGE 2
A-121 VCF 2 System A - 100 doepfer Controls: 2. VCF 2 - Overview 1 Audio Level : Input signal attenuator VCF 2 MULTIMODE FILTER Audio In Audio Level ➊ ➋ Notch 0 10 0 10 Freq. High FCV 2 0 Band 10 Res. 0 Low ➃ 10 QCV 2 ➒ QCV 2 0 2 ➂ QCV 1 ➑ ➎ ➁ FCV 2 ➐ ➍ Cut-off frequency control 3 FCV 2 : Attenuator for filter CV § 4 Res. : Resonance control 5 QCV 2 : Attenuator for resonance CV % FCV 1 ➏ ➌ ➀ 2 Freq.
PAGE 3
System A - 100 doepfer High Pass 3. Basics Low Pass The most common type of filter in analogue sound production is the low-pass, which filters out the higher parts of the sound spectrum, and lets the lower frequencies pass unchanged. Cut-off frequency fC determines the frequency at which this occurs (see Fig. 1). Out Low Pass fc Out Out High Pass Freq. Band Pass fc VCF 2 A-121 Freq. fc Out Band Pass In a band-pass filter, both ends of the frequency spectrum are attenuated (see Fig.
PAGE 4
A-121 VCF 2 System A - 100 Resonance Another filter parameter is resonance, also known as emphasis or Q. As the value for Q gets higher, the frequencies around the cut-off frequency fC are emphasised. Fig. 2 shows this process using a low-pass filter as an example (a high-pass filter would produce a mirror-image). This way, you can make the frequencies around the cut-off point stand out more. In band-pass mode, an increase in Q’s value makes the bandwidth narrower.
PAGE 5
doepfer System A - 100 VCF 2 A-121 1 Audio Level Close to the maximum position, the filter goes into self-oscillation. In this mode it behaves like a sine wave oscillator, and can be used as an alternative sound source. This attenuator controls the input level of the signal to be filtered, entering the module at input ! . 5 QCV 2 4. Controls H If the filter’s output signal is distorted, turn this control down, unless the distortion is wanted as a special effect.
PAGE 6
A-121 VCF 2 System A - 100 5. In / Outputs ! Audio In This socket is the filter’s audio input. Patch the output of a sound source (such as a VCO, noise generator or mixer) into it. " FCV 1 Socket FCV 1 is a voltage control input for the filter frequency. It works to the 1 V / octave standard (like a VCO). If you patch a modulation source (eg LFO, ADSR) to this input, the cut-off frequency of the filter will be modulated by its voltage: ie.
PAGE 7
doepfer VCF 2 A-121 System A - 100 6. User examples Spatial manipulation of the spectrum The A-121’s cut-off frequency can be modulated in a variety of ways: Fig. 3 shows an interesting application of the multimode filter. Each of the four outputs is fed to one corner of a quadraphonic sound stage (VCAs and amplifiers, etc. have been omitted for the sake of clarity). • VCF - LFO Modulation of the cut-off frequency produces cyclical changes of the sound spectrum. At low frequencies (c.
PAGE 8
A-121 VCF 2 System A - 100 Generating vocal effects With the patch in Fig. 4 (see next page) vocal effects can be produced, using two A-121 filters. A sawtooth at around 100 Hz or less is patched into two A-121 filters. Set Q to a small or medium level, and use different mid-frequencies for each of the two filters. Modulate the VCO and both filters with a triangle wave LFO at about 1 Hz, but with the voltage input to one of the filters inverted by an A-175 inverter.
PAGE 9
VCF 2 A-121 System A - 100 doepfer A-121 Band A-138 CV A-121 VCO CV 2 Gate A-131 Band CV 3 ADSR LFO A-175 A-132 Controller CV Fig. 4: Producing vocal-like sounds P Check out various different combinations of mid-frequency settings on the filters. Experiment with different envelope settings. P By turning down the pitch CV input to the VCO, more speech-like intonation can be achieved.
PAGE 10
A-121 VCF 2 System A - 100 doepfer 7. Patch-Sheet The following diagrams of the module can help you recall your own Patches. They’re designed so that a complete 19” rack of modules will fit onto an A4 sheet of paper. Photocopy this page, and cut out the pictures of this and your other modules. You can then stick them onto another piece of paper, and create a diagram of your own system.