Elara
Introduction
Elara is a real-time software synthesizer for PC compatible machines running Linux. Elara is designed to replicate an analogue synthesizer, and has a very comprehensive voice architecture.
The main features include:
i) Two independent audio oscillators per voice - with cross
modulation and sync.
ii) Two independent envelope generators - with keyboard tracking.
iii) A low frequency oscillator - with variable delay.
iv) A resonant low pass filter - with switchable -12 dB/octave
or -24 dB/octave cutoff slope and variable keyboard tracking. v) A variable high pass filter - with a -6 dB/octave cutoff slope.
Requirements
The synthesizer requires a 16 bit sound-card, X (with at least a 16 bits per
pixel display), and a working sound driver (the synth has only been tested
with the OSS driver). The synthesizer works best on fast machines, and is
probably not usable on anything less than a Pentium class machine.
The number of playable notes is a function of the machine speed and the sample
rate selected in the configuration file. For example, the development
machine, a Cyrix 6x86 P200+, manages one note with an output sample rate of
44,100 Hz.
Elara may be played via an external MIDI keyboard, or MIDI events may be sent
to the synth via a named pipe.
Installation
The executable (elara) may be put anywhere in the user's path. The small script install.sh should be run as the synth user (not as root). This script places a configuration file .elararc and a directory .elara (which is used for patch storage) in the user's home directory. Forty sample patches are placed in the .elara directory. Elara will look in the home directory of the current user on startup to find this configuration file and patch directory. If Elara cannot find the patch directory then patch saving will not be possible.
To optionally improve the audio performance, real-time scheduling for Elara may be enabled. The elara executable should be modified as follows (this must be done as root):
chown root elara
chmod u+s elara
Configuration
The configuration file (.elararc) contains values of the five parameters that may be set by the user. If this file cannot be found by the synthesizer then default values are used. The parameters are set, one per line, by equating the parameter with a value, eg:
user_parameter = value
Whitespace is ignored, as is all text between a # and the end of a line, eg:
# this is a legal comment
user_parameter = value # this parameter will be set
# the following parameter will not be set # user_parameter = value
The five user parameters are:
midi_device - This is used to set the MIDI input to the synthesizer. This
should be a path and device/fifo name. The default is /dev/midi.
dsp_device - This is used to set the audio output for the synthesizer.
The default is /dev/dsp.
midi_channel - This is used to set the MIDI receive channel. Valid values
are numbers 1 to 16 or the word all to receive on all channels.
The default is all.
polyphony - The maximum allowed number of simultaneous notes is set using this
parameter. The number allowed includes the notes that are
releasing. Notes played after the maximum has been reached will
cutoff the oldest releasing note or, if no notes are in their
release phase, the oldest held note. The polyphony value should,
if possible, be set to at least twice the expected number
of held notes - so that notes may have some chance of decaying
naturally. The default is 1.
sample_rate - The number of sound samples per second produced by the synth is
set by this parameter. A high value gives good sound quality
and low latency, but is more demanding in terms of processing
power required. For low end Pentium machines a compromise
between polyphony and sample_rate will be required.
The default is 44100.
If polyphony or sample_rate is set to a value that is too high the machine will not be able to keep up with the required rate of sound sample production. When this happens a "buffer underrun" occurs. If a buffer underrun is detected by the synthesizer then notes are killed until no further underrun occurs. A buffer underrun might be audible, so care should be taken in selecting the sample_rate and polyphony values. One approach to setting these values is to set the sample rate to a value that gives acceptable sound quality, then use a CPU monitor such as top to show the amount of CPU time used by the synthesizer. Notes should be progressively held until the total CPU load is somewhere between 50% and 75%. The number of held notes is then the maximum polyphony value for the machine at the selected sample rate.
Using Elara
Elara may be started by typing elara at the command prompt. Elara should ALWAYS be closed by using the POWER switch located at the bottom left of the control panel. Failure to shutdown Elara correctly may leave stray processes running on the system. It will then be impossible to restart Elara without manually killing these processes. If it is suspected that this has happened then all processes named elara should be killed manually before restarting.
Using Elara should be easy for anyone that is familiar with analogue synthesis, and a tutorial on subtractive synthesis will not be given here. The control panel is split into three main regions, the top two of which control the basic sound made by the synthesizer. On the third panel are the controls for BEND and additional LFO MODulation, as well as the patch memory controls, the MASTER TUNE and VOLUME controls, and the POWER switch.
Elara receives and responds to MIDI pitch bend and modulation information according to the settings on the BEND and LFO MOD controls. MIDI pitch bend may be used to modulate the pitch of the oscillators and the cutoff frequency of the low pass filter. The sliders in the BEND section control the amount of bend applied (0 to +/- 1 octave for the oscillators), and the switches allow the bend to be applied to any combination of oscillators and filter. The MIDI modulation parameter is used to trigger the additional LFO modulation for trill effects. Any value of the MIDI modulation parameter greater than zero will trigger LFO modulation. The LFO modulation will rise to the maximum level set by the corresponding sliders at a rate determined by the LFO MOD RISE TIME control. The VCO MOD and VCF MOD switches allow LFO modulation to be applied to either the pitch or the filter cutoff frequency.
Patches are loaded by pressing three of the numbered buttons below the patch number display. To load patch 1 the buttons 0, 0, and 1 should be pressed; to load patch 123 the buttons 1, 2, and 3 should be pressed. To write a patch the WRITE button should be pressed, followed by three numbers corresponding to the new patch location. Patches may also be copied in this way. For example, to copy patch 11 to patch 123 the sequence would be:
i) Load patch 11 (by pressing 0, 1, and 1).
ii) Press the WRITE button.
iii) Press buttons 1, 2, and 3.
Patch 11 will now be copied to patch 123.
To cancel writing the WRITE button should be pressed again before three number buttons are pressed. Valid patch numbers are in the range 0 to 127. Patches are also selectable via MIDI.
Problems
Distorted sound when playing many notes or with the filter resonance control at a high position.
- Clipping of the output signal, try reducing the VOLUME or VCA LEVEL.
Periodic distortion or distortion present in the sound when using the panel or other windows.
- Try switching on the real-time scheduling, ie (as root):
chown root elara
chmod u+s elara
Comments and Suggestions
Email to elara_synth@yahoo.co.uk
Warranty
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.