
doepfer a1891 voltage controlled bit cruncher / modifier
price : $140.00


module a1891 is the first derivative of the universal ad/da module. it offers several voltage controlled algorithmic functions like voltage controlled bit crunching, bit
shifting (with/without carry over), bit exchange, rectifying, absolute value and calculating operations like addition, subtraction, multiplication or division.
the module has two control units both with manual control and cv input with attenuator:
one for the algorithmic function according to the selected mode (e.g. number of shifted bits): bc and bc cv
and one for the sampling rate (sr and sr cv).
the signal input is equipped with an attenuator. as the module is dc coupled even control voltages can be processed.
the mode (e.g. bit crunching, bit shifting, bit exchange) is selected by a 16position rotary switch:
switch position 
function 
remark 
1 
bit crushing 
bc controls the number of bits (bit
reduction) 
2 
and 
signal and bc 
3 
or 
signal or bc 
4 
xor 
signal xor bc 
5 
bit shift right 
bc controls the number of bit shifts 
6 
bit shift left 
bc controls the number of bit shifts 
7 
multiplication 
signal x bc 
8 
compare & complement 
if signal > bc then output = bit
complement of the input signal, otherwise unchanged 
9 
compare & absolute 
if signal > bc then output = absolute
value of the input signal, otherwise unchanged 
10 
addition 
output = signal + bc (with
overflow/clipping) 
11 
addition with bc swap 
same as 10 but with nibble swap of bc
(nibble = half byte, i.e. four bits) 
12 
short delay 1 with dynamic normalization 
bc controls the length of the delay memory 
13 
short delay 2 
same as 12 but different length/feedback 
14 
short delay 3 
same as 12 but different length/feedback 
15 
short delay 4 
same as 12 but different length/feedback 
16 
four stages fir filter 
bc controls the filter coefficient 
sound examples:
these are the first sound examples of the a1891 prototype we will show at the namm in january 2008. christian assall has programmed 16 different operating modes that are
selected by the 16position rotary switch. the simplest mode (mode #1) is the standard bit crunching function. the other modes are different bit manipulation modes. these are the
very first trials and the modes of the final version of the module may be different. for all demo sounds the triangle output of a vco was used as signal input for the a1891.
for clarity no other sound processing modules are used. the sound is generated only by an vco and the a1891. the vco pitch is controlled by an a155 sequencer.
the first example shows the effect of manually changing the sampling rate in mode #1
the second example is a presentation of the 16 modes available in the prototype. one after another each of the 16 modes is selected. the
sampling rate is fixed, only the manual bc control is operated from ccw to cw and back to ccw for each mode
the third example shows the effect of dynamic sample rate modulation. an adsr is triggered by one of the trigger rows of the a155.
the adsr output is connected to the sr cv input to modulate the sampling rate by the adsr envelope. the bc parameter is fixed.
in the next example the adsr output is connected to the bc cv input. this example shows the effect of dynamic bc modulation. the sample rate
is fixed
in this example a vca has been added between the vco output and the signal input of the a1891. the adsr output is connected to the cv input of
the vca. this example shows the effect of dynamic input level modulation. in addition the sample rate has been reduced a bit manually at the end of the example
the following samples arised from playing around with the a1891. the patch is the same as
above but the adsr is used for both controlling the vca and the bc cv input of the a1891 (inverted output of the adsr for bc). several parameters have been changed manually
during the examples (mainly envelope amount and offset controls of the vca and the a1891).
more demos made by our a100 customer herman pearl/soy sos (tuffsoundrecording.com) can be found there:
http://share.ovi.com/media/soysos.public/soysos.10001
http://share.ovi.com/media/soysos.public/soysos.10003
http://share.ovi.com/media/soysos.public/soysos.10004
http://share.ovi.com/media/soysos.public/soysos.10005
this module has a maximum current draw of 50ma. it requires 8 hp/te worth of space to fit in a eurorack frame.
