Logidy EPSi User manual

EPSi Effect Processor
User’s Manual
l gidy

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Table of Contents
Table of Contents..................................................................................................2
Document revisions ..............................................................................................3
Introduction ...........................................................................................................3
1. Presentation...................................................................................................4
1.1. What is the EPSi? ......................................................................................4
1.2. What is Convolution? .................................................................................4
2. Plugging In.....................................................................................................4
2.1. Power Jack.................................................................................................5
2.2. Audio Inputs ...............................................................................................5
2.3. Audio Outputs ............................................................................................5
2.4. SD Card Slot ..............................................................................................6
3. EPSi User Interface .......................................................................................6
3.1. Firmware Version .......................................................................................6
3.2. Changing Parameter Values ......................................................................6
3.3. Foot Switch ................................................................................................7
4. Parameter List ...............................................................................................8
4.1. Version 1.00 Parameter List.......................................................................8
4.2. Version 1.00 Algorithm...............................................................................8
4.2.1. Quality ....................................................................................................8
4.2.2. Stereo image generator ..........................................................................9
4.2.3. Adding some life to linearity....................................................................9
4.3. Version C.00 Parameter List ....................................................................10
4.4. Version C.00 Algorithm ............................................................................10
4.4.1. Quality ..................................................................................................10
4.4.2. Stereo operation ...................................................................................11
4.4.3. Tone Controls .......................................................................................11
5. Managing Impulse Response Files..............................................................11
5.1. SD Card and File Format .........................................................................11
5.2. EPSi “EPDA” Folder.................................................................................11
5.3. File Naming Convention...........................................................................12
Appendix A: Specifications .................................................................................13
Appendix B: Error Codes ....................................................................................14
Appendix C: Impulse Responses List (IR V1.00) ................................................15

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Document revisions
Dec 1 2013: Original draft. EPSi firmware 1.00
Jan 10 2014: Added a few details
Jan 13 2014: Fixed error “128 samples”
Feb 19 2014: Added support for Version C.00
Introduction
Thank you very much for purchasing a Logidy EPSi Effect Processor. We hope
you find our product an inspiring tool in your quest toward musical bliss. You will
find in this document all the information you might need to get the best out of our
product.
Lets’ get started.

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1. Presentation
1.1. What is the EPSi?
The Logidy EPSi Effect Processor (EPSi from now on) is a DSP powered effects
processor packed in a small pedal format. The interface and the inner workings
of the EPSi are not tied to a particular application. Actual parameter names only
show on the 3 character LED display and can be changed. And because the
firmware running on the pedal is easily replaced via an SD Card, the EPSi can be
turned into many different things.
As of now there are two versions of firmware available for the EPSi:
- Version 1.xx: This version is optimized for reverb sounds.
- Version C.xx: This version is optimized for cabinet speaker and room
sounds.
Both versions make use of convolution and the SD Card to load sounds.
1.2. What is Convolution?
The behavior of a linear time invariant system (like an acoustic hall or a linear
EQ) is fully described by its impulse response. An impulse response can be
obtained by recording the sound coming out of such a system when an impulse –
a kind of short pop – is applied to it. Once this impulse response is acquired, the
behavior of that system can be recreated by convolving that impulse response
with an input signal in a process that is equivalent to filtering. To simulate
acoustic reverberation sounds the time window of that filter is as long as the
decay of the effect. This leads to high computational requirements for long decay
times. In the reverb version of the firmware we are able to reach windows of
about 6 seconds in duration, which is long enough to simulate an acceptable
variety of sounds found in nature or in devices trying to mimic it.
Version C of the firmware is optimized for zero latency convolution and dual
channel processing. This leads to a reduce time window of 1.5 second.
2. Plugging In
If you have used effect pedals in the past, you will find that incorporating the
EPSi works pretty much the same way as with any other pedal. The EPSi
features 4 audio connectors on the back - 2 stereo pairs, one for importing

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analog audio into the pedal and one producing analog audio out, as well as a
power jack. The connectors are laid out as shown here:
L(M) OUT R L(M) IN R
9V DC
2.1. Power Jack
Connect the included 9 Volt power supply to an AC outlet and to the power jack
at the back of the unit. The EPSi uses the most common voltage polarity for
effects pedals with the positive potential on the outside sleeve of the connector.
Caution: When using a different power supply, make sure it conforms to the
specifications given at the end of this document. Insufficient or excessive
current/voltage can easily result in damaging the electronic circuits inside the
pedal and render it inoperable.
As soon as the EPSi is powered, it will start right away and go through its startup
sequence. See the user interface section for more on this.
2.2. Audio Inputs
Facing the back of the unit, the input connectors are on the right. The EPSi can
take in either a mono or a stereo signal. If a single jack is plugged in the L(M)
input – which stands for “Left(Mono)” – the signal coming from that input will be
copied onto the right side channel creating an internal split. If a single jack is
plugged in the R input – which stands for “Right” – no direct signal will go to the
left side channel. The impedance of the input stage is set so that an electric
guitar can be plugged in directly without suffering much loss in brightness in the
sound.
EPSi features an analog direct path so as not to add any latency to the dry
signal. This dry path can be disabled through the user interface.
2.3. Audio Outputs

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Facing the back of the unit, the output connectors are on the left. Plugging a
single jack into the L(M) connector – which stands for “Left(Mono)” – has no
effect on the dry path, but causes the left and the right channels of the processed
audio to be summed.
2.4. SD Card Slot
The EPSi uses impulse responses stored on an SD Card. The unit arrived to you
with an SD Card pre-loaded with a collection of impulse responses. If, on power-
up the EPSi does not detect the presence of a card, a test impulse response
generated internally is used instead. Cards can be inserted and removed while
the unit is running. Each time a card is inserted, the system will inspect its
contents and adapt accordingly without interrupting the audio processing. SDHC
Cards are currently not supported.
3. EPSi User Interface
The EPSi features a simple user interface including an endless value rotary
control, a button for stepping through parameters, a foot switch and a 3 digit LED
character display.
Note: Because the front panel of the EPSi does not explicitly name parameters,
it is possible for us to add/remove/change parameters in software. Make sure
that the version of this document matches the version of the firmware that is
running on your EPSi.
3.1. Firmware Version
On power up the EPSi first displays the version number of the firmware being
currently run. If an SD Card is present the system will quickly proceed with the
file initialization and take over the display. If a card is not present, the firmware
version number will show until the user interface is interacted with.
The Firmware on the EPSi can be replaced via the SDCard. Exact details on how
to perform a firmware update are provided on our website along with the new
program file.
3.2. Changing Parameter Values
Parameters on the EPSi are changed one at a time by stepping through them
with the “Param” button and using the “Value” knob.

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A single push on the “Param” button causes the display to reveal the name of the
current parameter. That name shows as long as the button is pushed and for
about 2 seconds after the button is released. After that the display reverts to
showing the value for that parameter. If the button is pushed again within the 2
seconds, the next parameter in the list becomes current and its value can be
changed with the “Value” knob. When the last parameter is reached, the stepping
loops back to the first parameter.
Exception: Recalling an Impulse Response
In the case of the first parameter the “param” button is also used to trigger the
loading (“Recalling”) of a new impulse response. When the value shown for the
first parameter does not match the index of the currently loaded impulse
response, the display will alternate between the value and “rcL” as shown here:
“rcL” stands for “recall” and will flash 4 times for about 5 seconds. If the “param
(Recall)” button is pushed during that time, the system will interrupt audio
processing and load the new impulse response. If the button is not pushed during
that time, the display reverts to showing the current impulse response index
number and stepping though parameters can resume.
3.3. Foot Switch
The foot switch on the top panel act as an effect enabling/disabling control. When
the effect is bypassed the display shows the following symbol:
Disabling the effect is equivalent to disabling the input of the effect. This means
that its trail will still be heard for some time after the foot switch is pressed.
While the effect is disabled access to parameters is still possible. When the user
interface is accessed the display reacts accordingly, but the display eventually
reverts to showing the symbol shown above.

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4. Parameter List
4.1. Version 1.00 Parameter List
Display Meaning Values
1.Sd The Index of the SD
Card File used as an impulse
response
The values available
depend on the contents of
the SD Card (see file
naming section)
2.FL FX Level. The level of the
processed audio AKA “wet”
level.
Unit: dB.
Range: -40dB to +10dB
Actual resolution: 0.25dB
steps
3.rt Reverb Time. The decay
time in seconds for the impulse
response. This is the measured
RT60
Unit: seconds
Range: from 50% to 150%
of the nominal time of the
impulse response*
4.dr Dry Path Enable. The
state of the internal analog
direct path relay.
Unit: none
Range: on - off
* Increasing or decreasing the perceived decay is done by applying a volume
envelope to the impulse response. When increasing the decay time, the
envelope adds gain to the end of the tail also increasing whatever noise might be
in the file. This can sometimes make the tail sound unnatural.
4.2. Version 1.00 Algorithm
4.2.1. Quality
Convolution is a straightforward process. Although there are several ways this
process can be optimized for computational bandwidth, the end result can not
differ form the simple theory. At the root and with a large enough bit depth (32-bit
floating point in our case) all convolvers sound the same. The quality of the
sound generated largely depends on the quality of the impulse response used.
A peaky or fluttery impulse response form a low quality algorithmic reverb unit
will sound the same on the EPSi. However an impulse response from a very
diffused and uneven acoustic space will sound as smooth and transparent on the
EPSi.

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The collection loaded on the SD Card included with the EPSi has impulses from
many different high quality sources (acoustic, electronic, electromechanical, and
synthesized).
The maximum Impulse response duration is about 6 seconds (262144 samples
at 44.1 KHz). Only the first 6 seconds of data get loaded for longer duration files.
This can result in a very abrupt sounding cutoff if the wave does not include
some sort of fade out within that time span.
The processing latency of the wet path is about 10.0 ms. As pre-delays in reverb
sounds are often longer than this, the latency is not noticeable on reverb sounds.
For zero latency processing, see firmware version C.
4.2.2. Stereo image generator
In order to reach our 6 second time window the DSP can only process one
channel. The EPSi only uses the first channel of a multichannel wave file.
EPSi uses an original adaptive algorithm to synthesize a new stereo image. The
result of this process sounds as if the impulse was re-captured with an M/S
microphone pair and is convincing for most space simulation applications.
However any hard panning built in the original impulse is lost through this
process.
The stereo image generator is disabled when the right output jack is left
unplugged (mono output mode). In this situation the processed signal is an exact
rendering of the convolution.
4.2.3. Adding some life to linearity
Basic convolution is a perfectly linear process. It can not simulate any sort of
distortion or time varying effect. This can result in the output sounding somewhat
stale. To remedy this, the stereo image generator also includes a little bit of
detuning. The detuning amount is very slight (1.5 cent). The result is some subtle
added sense of motion and chorusing, widening and warming up the sound with
no audible pitch shifting.

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4.3. Version C.00 Parameter List
Meaning Values
1.Sd The Index of the SD
Card File used as an impulse
response
The values available
depend on the contents of
the SD Card (see file
naming section)
2.Lo Low frequency tone
control level
Unit: none.
Range: 0.0 to 10.0
3.Md Mid frequency tone
control level
Unit: none
Range: 0.0 to 10.0
4.Hi High frequency tone
control level
Unit: none
Range: 0.0 to 10.0
5.LF Low frequency tone
control cutoff
Unit: KHz
Range: 0.01 to 9.90
6.HF High frequency tone
control cutoff
Unit: KHz
Range: 0.01 to 9.90
4.4. Version C.00 Algorithm
4.4.1. Quality
The algorithm in Version C is optimized for zero latency processing. The actual
latency measured from analog input to analog output is 1.04 ms, 80% of this is
due to the group delay of the anti aliasing filters of the A/D and D/A converters. A
maximum convolution window in stereo of 1.5 sec (65536 samples) can be
achieved.