Abstrakt Instruments Avalon Reference Manual
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Contents
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12 AVALON - Reference ManualThe frequency response of the audio signal to the final amplifier inthe TB-303 (and hence the Avalon w/ default setting) is limited to ~70Hz.This was done to maximize the signal-to-noise performance of the TB-303 by removing the low frequency component of the signal that woulddrive it into clipping faster. If exact TB-303 clone behavior is desired thisswitch should be left in he 'out' position. However, for a full-rangeresponse, especially when using the sub oscillator, you may want toextend the frequency response.3.4 FILTER ENVELOPEThe filter envelope is a simple decay envelope. ENV MOD controlsthe depth of the envelope modulation. ACC DECAY and ENV DECAYset the decay time of the filter envelope for accented and unaccentednotes respectively. In both cases the decay time can be adjustedbetween 200ms and 2s.The implementation of the filter envelope and filter modulation ingeneral is non-standard. For specific details please see Appendix B.The original TB-303 does not allow the filter envelope modulation tobe turned all the way off. The Avalon has an internal switch setting thatallows the filter envelope depth to maintain the TB-303 behavior. SeeAppendix A for details.When an accent has been programmed (or played) an additionalcontrol voltage (envelope) is sent to the filter and final amplifier(VCA). First, a copy of the filter envelope is sent to the VCA controlinput to give a volume boost on accented notes. Second, a slewedcopy of the filter envelope is sent to the filter control input. This isresponsible for the characteristic wow sounds you can get withaccented notes. The character of this slewed version also varies withthe setting of the RESONANCE control, as increasing resonance alsoincreases the slew of this control voltage. The depth of this additionalaccent modulation is determined by the ACCENT control.For specific details on the behavior of accents on the filter andamplifier see Appendix B.3.5 AMPLIFIERVCA DECAY sets the decay time of the final amplifier (VCA) envelope.The control ranges from off to 4s decay time.The VCA Envelope is identical to TB-303. While the decay time isvariable in the case of the Avalon, the attack is fixed to retain thebehavior of the TB-303. This envelope can be turned completely off bysetting VCA DECAY to the minimum setting.3.6 MODULATION ENVELOPEThe modulation envelope is an additional attack-decay (AD) envelopethat can be used to modulate the filter and the final amplifier (VCA).In addition to the dedicated filter and amp decay envelopes, thismodulation envelope allows for more complex modulation. Themodulation is bipolar and the envelope can be triggered on any stepof a sequence and manually in REALTIME modes.ATTACK and DECAY set the attack and decay time of the envelope.The attack time ranges from 0.9ms to 6s. The decay time ranges from1.7ms to 10s.VCF DEPTH and VCA DEPTH sets the amount of positive (+) ornegative (-) envelope modulation to the filter and VCA respectively.VCF DEPTH has been designed with a progressive voltage offset forincreasing (+) or (-) modulations amounts. When the control isrotated clockwise for (+) modulation a negative offset is applied tothe filter control input. Likewise, as an increasing (-) modulationamount is set by rotating the control counter-clockwise a positiveoffset is applied to the filter control input. See Appendix B for moredetails.VCA DEPTH has been designed with a progressive voltage offset fornegative (-) modulation amounts. When the control is rotatedcounter-clockwise for (-) modulation a positive offset is applied to theVCA control input. See Appendix B for more details.The VCA Depth implementation as described above and in AppendixB allows the VCA to be opened (drone mode) by setting the control formaximum (-) modulation.A key feature of the Avalon is the triggering of the modulationenvelope via the sequencer. The term "MOD ENV" as used in this manualrefers to programming or playing a modulation envelope trigger. Thisshould not be confused with "ENV MOD" , which is the name given to thefilter envelope depth control.3.7 OUTPUTVOLUME controls the output level .There is a discrete "mixer" stage after the volume control. This is acarryover from the TB-303 which has a Mix Input before the output jack.In order to retain the same behavior the Avalon incorporates this samecircuit. This stage clips asymmetrically and can clip easily. If you hearunwanted distortion in the main or phones outputs try turning down thevolume control. |
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