21
SUMMIT: SIMPLIFIED BLOCK DIAGRAM
FPGA
Voice 1
Osc 1
Osc 2
Osc 3
Voice 16
Osc 1
Osc 2
Osc 3
Analogue
Sum
Filter
12dB
Filter
12dB
Filter
Pre Filter
Overdrive
Pre VCA
Distortion
Left VCA
Right VCA
Analogue
Sum
Filter
12dB
Filter
12dB
Filter
Pre Filter
Overdrive
Pre VCA
Distortion
Left VCA
Right VCA
VCA
Sum 16
VCA
Sum 1
Overdrive
Left
(Analogue)
Overdrive
Right
(Analogue)
Sum
Audio Inputs
Summed to mono
FX Left
(FPGA)
FX Right
(FPGA)
Sum L
Sum R
Main or Aux Left
Main or Aux Right
Summit’s architecture essentially comprises two complete, identical, but entirely separate
synthesisers with a single set of controls. Depending on the type of Patch in use – Single
or Multi – the two synths either work in an identical manner, with each control affecting the
same parameter in both synths simultaneously (Single Patches), or they work differently, to
generate Parts A and B of a Multi Patch, with each control affecting its parameter in only
one of the two synths at a time.
Each of Summit’s two Parts uses eight separate voices, which are treated independently
throughout the remaining signal chain. The voices are synthesised digitally in a Field
Programmable Gate Array (FPGA) using Numerically Controlled Oscillators running at an
extremely high clock rate, resulting in waveforms which are indistinguishable from those
using traditional analogue synthesis.
Each voice is a mix of the outputs of the three oscillators; when you adjust one of the
oscillator level controls
38
,
39
or
40
you are effectively adjusting the level of eight voices
simultaneously. The subsequent elements in the signal processing chain are entirely in the
analogue domain. Note that distortion can be added in several places – before the filter
(Overdrive
62
), after the filter (FltPostDrv in the Voice Menu) and after final voice
summation (Distortion Level
68
). The sonic effect can be quite different in each case.
Note that the time-domain effects (FX) – chorus, delay and reverb – are digitally generated
within the FPGA as well. The stereo effects send into the FX processing section is taken
from post the main VCA, so all distortions added to the signals are processed by the FX.
The FX return signal is added back to the same point in the signal path.
External inputs
Summit also has a pair of audio inputs (see
10
at page 9): these allow you to connect
external audio sources – e.g., from other synth modules - and then use Summit’s extensive
processing capabilities to treat their sounds. The two ¼” jack sockets are intended for the
left and right signals of a stereo pair, but you can connect a mono source to the LEFT input
only if you wish.
Page 3 of the Voice menu enables these inputs and lets you choose whether the external
signals connected are to be mixed with each of the 16 voices at the input of the analogue
filter section, or to be added to the synth sound “post-VCA” at the output of the filter
section. The first option – PreFilt in the menu – effectively adds the external signals to
Summit’s own internally generated sounds, and they will therefore undergo the same signal
processing as the native synth sounds, including analogue Pre Filter Overdrive and Pre
VCA Distortion.
The second option – P o st Filt in the menu – lets you route the external signals directly
to Summit’s FX section, where they can either be added to the native synth sounds,
or have one of the FX sections allocated to them exclusively: this selection is made on
Page C of the Settings menu. Because the outputs of the FX sections may be routed to
either the main or auxiliary outputs, this allows you to add FX to external signals entirely
independently of any synthesiser functions.
To Next Page
Loading...
