shruthi-1

v0.97 --------------------------------------------------------------------------

SYNTHESIS

- The envelopes have a different behaviour - the attack does not reset 0 at the
beginning of each note, but rather starts from the current level of the
envelope.
- The way velocity is managed in the context of note priority handling has been
changed. When you play and hold a note, play a new note and release it, the
held note is retriggered with its original velocity.
- Phase increments are computed using a new interpolation technique, saving
1.3kb of code size.

FILTER BOARD HANDLING

- Support for the "LP2+Delay" filter board.

UI

- When using the programmer, the screen shows the value of the edited parameter.


v0.96 --------------------------------------------------------------------------

SYNTHESIS

- The LFSR used for the noise oscillator can now be reset by oscillator sync.
This allows the creation of pitched sounds with a very rich timbre.
- Constant values have been introduced in the mod matrix. They can be combined
with operators to attenuate, translate, or quantize a modulation source by a
known value.
- A Quantize operation has been added to the operators. It reduces the bit-depth
of a modulation source to create a Sample & Hold like effect on any modulation.
- A Lag processor operation has been added to the operators. It smoothes the
slope of a modulation source to create more progressive modulations.
- Two MIDI channel/note combo can be defined as "triggers". When such a MIDI
message is received, a note is not played. Instead, a modulation source
("trigger 1" and "trigger 2" in the mod matrix) changes. This can be used to
trigger effects (such as a pitch change or LFO speed boost) from a keyboard or
an external MIDI sequencer.
- 2 new modulation destinations, "env 1" and "env 2" allow the envelopes to be
triggered whenever a modulation source crosses a threshold.
- A new mixing mode, "duo", allows the synth to be used in a pseudo-duophonic
mode. The least recently played note is played on osc 2, and the most recently
played note is played on osc 1.
- 3 new mixing modes, "2 steps", "4 steps" and "8 steps" allow the oscillators
(or oscillators, sub-oscillator and noise source) to be triggered rythmically
at each note.
- A new mixing mode, "seqmix" allows the oscillators/sub/noise sources to be
rythmically disabled according to the pattern input in the step sequencer.
This allows very crude rythmic patterns to be programmed (using noise as a
snare drum and the sub-oscillator as a kick).
- The attack time modulation destination now accepts both positive (faster
attack) and negative (slower attack) modulations.

FILTER BOARD HANDLING

- The cutoff range of the Polivoks filter board has been shifted up by one
octave.
- Support for the "4-Pole Mission" filter board.

CODE

- 256 bytes have been saved by using the same table for the lowest octaves of
the triangle oscillator.
- 129 bytes have been saved by simplifying the "vibes" wavetable.
- A bug that caused random corruption of an unused memory area during program
startup has been fixed.
- 2.5 kbytes have been saved by de-specialization the Oscillators code.


v0.95 --------------------------------------------------------------------------

SYNTHESIS

- A page has been added to configure the routing of the Polivoks filter board.
- The page showing the hpf settings for the SSM2044 filter board simultaneously
displays the cutoff/resonance of the lpf - allowing both filters to be tweaked
at the same time.
- Added a cutoff-coupling mode for the dual SVF filter board.
- MIDI notes in the 120-128 range are no longer wrapped to 108-116.
- Fixed a bug causing a faint VCA bleed with some specific combinations of
modulation sources routed to the VCA.
- Added a new mixing mode, "fold", which equally mixes oscillator 1 and 2 and
send the output to a fold-back distortion, the amount of which is controlled by
"mix"
- Added a new mixing mode, "bits", which equally mixes oscillator 1 and 2 and
send the output to a bit-reduction distortion, the amount of which is controlled
by "mix".

CODE
- 512 bytes have been saved by using the same table for the lowest octaves of
the triangle oscillator.

UI

- Fixed a bug occurring when scrolling backwards from the second filter page.
- Fixed a bug preventing the tempo and LFO rate parameters to be edited with the pot, when the unit is configured in "snap" mode.


v0.94 --------------------------------------------------------------------------

SYNTHESIS

- Fixed a bug that caused a loudness drop of the vowel oscillator
- Fixed a bug that caused the filtered noise "oscillator" to output incorrect
values when the parameter was set to a high value.
- The envelopes now have a smoother curve, and slower attack / decay / release
times can be achieved.
- Fixed a timing bug that caused the main oscillators pitch to be off by 8
cents.

CODE

- The z-family oscillators now share common code, saving ~700 bytes of code.
- Resource table de-duplication saved ~200 bytes of code.
- The vowel oscillator code has been simplified by ~100 bytes.
- MIDI input is polled from the 39kHz audio interrupt rather than
interrupt-driven. This saves ~80 CPU cycles per byte of MIDI data received,
since there is no extra ISR intro/outtro when a MIDI byte is received.

MIDI IMPLEMENTATION

- The Shruthi-1 now uses an officially registered manufacturer ID for SysEx
communication. As a result, patch dumps/backups made with previous versions will
still be readable with v0.94 and onwards, but patch dumps made with v0.94 won't
be readable with earlier versions.
- CC90 and CC87 can be used to control the cutoff frequency and resonance of the
second filter on the dual SVF filter board.


v0.93 --------------------------------------------------------------------------

SYNTHESIS

- A menu has been added to control the routing of the dual SVF filter board.
- The wavetable synthesis code has been rewritten to allow interpolation
between waveforms which are not contiguous in memory. This allows the definition
of wavetables which are a subset, or a permutation, or a mix of the existing
wavetables. 10 such wavetables have been added to oscillator 1, approximating
classic Waldorf Microwave wavetables.

MIDI

- Upon reception of a program change, the active patch number is updated (in
v0.92, the patch was loaded but the patch number was not changed).

CODE

- Removed some cruft left after the oscillators rendering rewrite of v0.92.
Saved 110 bytes of code.
- The classes and functions in the 'hal' directory are now an independent
project called AVRil.
- I/O pins are now referenced by port/bit rather than by an Arduino-style pin
number.


v0.92 --------------------------------------------------------------------------

UI

- Patches can be tweaked from the load/save page. In this case, the 4 knobs have
the functions assigned to them in the performance page for this patch.
- The Shruthi-1 can be configured to boot directly on the presets page (aka
"presets mode").
- Non-blocking ADC scanning increases UI responsiveness.
- The "mix" and "osc 1" pages have been modified. The sub-oscillator settings
are now on the same page as the oscillator 1 settings.
- Holding the load/save switch (S6) pressed down while rotating the encoder
allows the values to be incremented/decremented by steps of 10.
Useful for browsing patches!
- Patches / sequences loading and saving can now be linked together (loading
patch 15 simultaneously loads sequence 15...). This can be enabled/disabled by
pressing S6+S5 in the load/save page.

SYSTEM

- Different options are available for using the 4 CV: 4 CV ins (assignable in
mod matrix -- default setting), 32-knobs programmer, or simple mapping to
cutoff, param1/param2 for pedals and joystick.
- External eeproms larger than 64kb are supported, up to 512kb. Note that when
a 512kb eeprom is used, the last 64kb block is not used (this is due to the
fact that 16-bit arithmetic is used to compute addresses, and that the
address space includes the 16kb of the internal eeprom).

MIDI

- SysEx Patch request command (0x11 0x00). Upon reception of this command, the
Shruthi dumps the currently edited patch. Might be useful for an editor!
- SysEx Patch write command (0x21 0x00 0xnn 0xnn). Upon reception of this
command, the Shruthi writes the current patch to a target memory.
- Support for NRPN increment/decrement.
- The SysEx backup protocol has been extended to support backing up / restoring
more than 16kb of patch data.
- A bank and program change message is sent whenever a preset is loaded.
- Bank change messages are handled, to allow patches above 128 to be loaded.
- Volume change messages (CC 7) are handled.
- A new MIDI out mode has been added in which only user-initiated knobs
changes are sent to the MIDI out. This mode is ideal for using the Shruthi with
both its IN/OUT ports connected to the same device. The other modes are not
suitable for operation in this configuration since they can cause unwanted MIDI
loops.

SYNTHESIS

- The shape of the envelope (approximation of an exponential) has been refined.
- The "2 bits" modulation destination is gone, since there are now better ways
(extra TX pin, shift register out) to communicate with a filter board.
- A new modulation destination (replacing "2 bits") allows the attack of both
envelopes to be sped up. This settings is particularly useful when velocity
is used as a modulation source.
- The "digital silencing" of oscillators when envelopes have reached zero has
been improved. The oscillators are now digitally silenced whenever the VCA
destination in the modulation matrix has reached a value of zero.
- The noise source in the mixer is now refreshed at 40kHz instead of 10kHz,
giving it a richer timbre.
- The phase counters are now 24 bits instead of 16 bits. This allows more subtle
detuning effects between the oscillators, especially in the lowest notes.
- The audio engine has been rewritten from a "breadth first" to a "depth first"
perspective, and as a result, is faster.
- As a result of the audio engine rewrite, the vowel oscillator can now be used
with the noise and sub generators.
- The crossfading between wavetable zones is more subtle on the pulse
oscillator (square with a parameter > 0).
- To make more room for upcoming features, the waves wavetable has been
downsampled to 128 samples/waveform instead of 256.
- New mixing modes (>>4, >>8) allow the oscillators signal to be
bitcrushed (sample rate reduction with a S&H) before being sent to the filter.
- A new feature ("operators") allows 2 pairs of modulation sources to be
combined through a variety of mathematical operations (addition, multiplication,
comparison) to yield two new complex modulation sources.

CODE

- Various code size optimizations saved 1kb.
- The modulation matrix processing code has been simplified.
- Changed compilation flags to achieve smaller code size.
- A menu in the UI and code infrastructure is ready to provide filter-board
specific menus and parameters in future firmware revisions.


v0.91 --------------------------------------------------------------------------

- Improved encoder debouncing/decoding algorithm.
- Changed "load" label to "browse" in patch load/save page.

v0.90 --------------------------------------------------------------------------

- Original release.