the fundamental and second harmonic at equal amplitudes when the pitch bend signal is close to zero. Otherwise
only the fundamental frequency can be heard. Therefore, you can find the ideal situation when there is zero voltage
at the pitch bend input - and it thus has no effect on the note - by adjusting
adjust 1
when
slider 16
is up until you
hear both. If you need to adjust the pitch bend offset so large that only the fundamental is heard, then you have to
remember that disconnecting pitch bend will change the tuning.
Grounding, shielding and RF interference
Inputs
The Eurorack community is diverse, therefore the common grounding and signal shielding practices may not be
obeyed in all environments. There should be only one common ground between the different modules in a rack, the
bus ground strip. Multiple grounding points may generate ground loops that add noise to sensitive inputs. However,
typically patch cables also carry a signal ground in their sleeve contact. This is usually not a problem for such low
output impedance, large amplitude signals that are applied to e.g. the envelope inputs within the same rack.
However, in a case when signals from a remote rack are connected to the HG-16 inputs, large ground loops may be
created. The unwanted additional ground usually comes from a common power jack safety ground connection, so
the obvious remedy is to use systems with fully isolated power supplies. The secondary remedy is to use the HG-16
ground lift switches
. Note that there should still be at least one common signal ground, and hopefully close to the
most sensitive input. Therefore it may not be a good idea to lift all the switches, because then the possibly remaining
common ground may be close to some noisy power supply lines. The HG-16 ground lift switches correspond to
three regions in the circuitry. If you keep the circuit board positioned so that the ground lift switches are up, and
look from the backside of the system, the leftmost switch (no. 3) is connected to the
Modulation 1
input ground,
the middle one to
Modulation 2, CV pitch
, and
CV velocity
grounds, and the third to all the
envelope input
grounds. The switch levers are very short, so use a small sharp tool for lifting the levers.
Outputs
The HG-16 outputs have their signal grounds permanently connected. Because the signal output has a balanced
differential output, it does not necessarily need a separate signal ground, so if there are noise problems, use the
receiving amplifier ground lift switches. Or, if there are none, you can even disconnect the signal cable shield from
the ground (but only at the output side).
RF/EM Interference
The HG-16 has high speed digital circuitry, therefore special concern has been paid to prevent high frequency
emission to sensitive analog circuitry inside the same rack or outside it. All the inputs and outputs have RF filters
tuned to block high frequency signals. The module has grounded metal shielding on both sides: the front panel has a
grounded copper layer, and the backside has an iron grille. The exposed front opening at the sliders has the slider
support bars also grounded. When connecting the module in a (metal) rack, the attachment screws also connect the
chassis to the rack metal parts that are typically grounded, but separately from the signal ground.
PM vs FM
The HG-16 has two different periodic modulation methods, phase modulation (PM) used in several modes, and
frequency modulation (FM) used only in Mode 14. The difference of these methods in terms of resulting signal
characteristics is described in the following.
As the name suggests, PM varies the instantaneous phase of the sinusoidal signal by the modulating waveform. The
result is a controlled distortion that can be heard as increasing harmonics with increasing modulating signal
amplitude. Because several of the operating modes have the possibility to add independent modulation to distinct
harmonics, each harmonic will correspondingly be distorted, therefore creating very spectrally rich signals within
separately controlled spectral areas. Because the modulation is limited inside the base frequency period, all the
distortion components will remain harmonic (except for some modes that allow signal folding/aliasing with extreme
modulation).
FM adds frequency shifting modulation over an arbitrary period that is not limited within the modulated signal
period like in PM. Therefore the resulting spectrum is not limited to harmonics of the modulated signal. Most
percussion instruments have nonharmonic spectra, therefore FM is useful for generating percussive sounding
signals, e.g. when the modulation comes from an envelope generator signal with steep amplitude variations. In fact,
many instruments that are periodic in their steady state, have complex nonperiodic spectra within their attack and/or
decay periods. Such periods can easily be generated in the HG-16 because the modulation parameters can be
controlled with external envelope generators, even independently for each generated harmonic.
10