Thứ Hai, 29 tháng 8, 2011

The Architecture of the MidiVerb 4

The Architecture of the MidiVerb 4
What is a Configuration?
A Configuration is an arrangement of one or more effects. Each of the 256 internal
Programs in the MidiVerb 4 use one Configuration. There are 32 different
Configurations available, each of which fall into one of four categories. The four
types of Configurations are: Single, Double, Dual Mono and Multi Chain.
A Single Configuration consists of one effect. These Configurations utilize complex,
processor-intensive effect algorithms providing the best quality possible for each
effect type supported. There are different kinds of Single Configurations, including:
Mono-in/mono-out. These effects have a single input (both inputs summed
together) and a single output (routed to both outputs).
Mono-in/stereo-out. These effects have a single mono input and two outputs.
Stereo-in/stereo-out. These effects have two inputs and two outputs.
In each case, the dry, uneffected signal of both inputs are also routed to the outputs.
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Double Configurations consist of two “side-by-side” mono-in/stereo-out effects.
These Configurations are identified by the presence of a “+” in their name. In each
case, the Left/Ch. 1 input is routed to one effect, while the Right/Ch. 2 input is
routed to the other. The stereo outputs of both effects are then summed together to
the outputs. The dry, uneffected signal of both inputs are also routed to the outputs.
Dual Mono
Dual Mono Configurations provide two mono-in/mono-out effects, one for each
channel. These Configurations are identified by the presence of a “:” in their name
(Delay:Delay). The Left/Ch. 1 input is routed to the first effect, whose output is
routed to the Left/Ch. 1 output. Likewise, the Right/Ch. 2 input is routed to the
second effect, whose output is routed to the Right/Ch. 2 output.
These effects can be chained using a special feature called Cascade mode. Cascade
mode only affects Dual Mono Configurations, and routes the output of the channel 1
effect into the input of the channel 2 effect. The Cascade function can be turned on
and off from page 2 in Utility mode (see Chapter 5). In this case, the Left/Ch. 1
output provides only the channel 1 effect’s output, while the Right/Ch. 2 output
provides the output of channel 1’s effect routed through channel 2’s effect.
Note: If Cascade mode is turned on, the [RIGHT/CH. 2] input will be disabled for all
Dual Mono Configurations. This is because the channel 2 effect is being fed the
output of the channel 1 effect.
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Multi Chain
The Multi Chain Configurations provide two or three stereo effects, which are
connected in series; i.e. one feeding the next in the chain. These Configurations are
identified by the presence of one or two “->” symbols in their name (Example:
“Chorus->Real Room”). These individual effect types provide excellent sound
quality but are less processor-intensive than their Single Configuration equivalents,
since the Digital Signal Processor is accommodating more than one effect at a time. In
other words, the reverb effect in the “Delay->Realroom” Configuration is not as
“dense” as the Single Configuration called “Realroom”.
In the case of Multi Chain Configurations, the “Mix” parameter of each effect
determines what the following effect receives at its input(s). Example: It is possible to
use the “Delay->Room” Configuration (where effect 1 is a mono delay and effect 2 is
a reverb), and have only the dry, uneffected signal going to the second effect; this is
done by setting the first effect’s Mix parameter to 000% (this means none of its output
can be heard nor is sent to the second effect in the chain).
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Reverb Effects
Reverb is made up of a large number of distinct echoes, called reflections. In a
natural acoustic space, each reflection’s amplitude and brightness decays over time.
This decaying action is influenced by the room size, the location of the sound source
in the room, the hardness of the walls, and other factors. The MidiVerb 4 offers the
following types of reverberation:
Concert Hall
This is a simulation of a large concert hall. Halls tend to be large rooms with lots of
reflective surfaces, where sounds can swim around, changing timbre over time. This
is a classic reverb which sounds good on just about anything. Try it on vocals, drums,
acoustic, electric, or orchestral instruments.
Real Room
This algorithm gives you the sound of a medium size studio room. This algorithm
uses a lot of processing power for a rich sound and smooth decay. It compares
favorably to high end studio reverbs for its rich sound. The attack is also more
reflective. It sounds good on drums, keyboards and guitars.
Realroom & Room
These are less processor intensive versions of the Real Room effect, used in Multi
Chain and Dual Mono Configurations.
This algorithm simulates a very small room. It can be used when just a slight amount
of ambient character is needed to augment a sound. For example, if playing a solid
body guitar, use the Ambience effect to simulate the sound of an acoustic guitar’s
hollow body.
Plate Reverb
This is a simulation of a classic echo plate, a 4' by 8' suspended sheet of metal with
transducers at either end used to produce reverb. Popular in the 1970’s, it still prized
for its transparent sound, particularly on vocals and guitars. This algorithm uses the
most processing available for a truly realistic reverb plate simulation. It works well
for a lush lead vocal, piano, or guitar, especially when looking for a classic rock and
roll sound.
This reverb effect’s direction can be set either forwards or backwards. Selecting the
forward direction provides a classic “Gated” digital reverb sound. Selecting the
reverse direction gives you a backwards reverb sound. A popular trick in the 80’s
was to record the reverb with the tape flipped over, so it would play backwards in
the mix. The reverse reverb is a useful effect for drums and other percussive sounds –
— adding space without washing out the instrument.
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MidiVerb 4 Reference Manual 31
Reverb Parameters
Most of the reverb effects in the MidiVerb 4 operate under the same set of control
parameters, which are listed and described in this section. However, reverbs which
use more processing power (i.e. the Single Configuration reverbs) provide more
parameters which take advantage of their extra processing power; parameters which
are not found in the other, smaller reverb algorithms. For example, Reverberation
Swirl is a parameter found only in the Single Configuration reverb types. Here are
the reverb parameters:
The Reverb Decay determines how long the Reverb will sound before it dies away.
When using the Reverse Reverb effect type, the Reverb Decay parameter controls the
Reverse Time.
Low Pass Filter
The lowpass filter that can be set between 059 Hz and 36.2 kHz, and attenuates all
frequencies above this value by 6dB per octave. The lower the setting, the less high
frequencies of the input are allowed to pass thru to the reverb effect.
All the reverb effects have pre-delay parameters. Pre-delay slightly delays the reverb
itself up to 175 ms, so that the dry signal more easily stands out from the reverb. A
bit of pre-delay can make certain instruments (such as snare drums) sound bigger.
Pre-delay Mix
This allows you to balance the amount of Pre-delay to Direct Signal as a percentage
of each. This gives you the ability to hear a bit of the Reverb before the loudest part
of the Reverb (the Pre-Delayed Reverb) sounds, and makes for a bigger, smoother
sounding Reverb.
Density controls how the first reflection of the reverb effect will appear. When set to
0, the first reflection is heard alone without any other reflections. When set to 99, the
first reflection appears to “fade-in” and then “fade-out”. This is because a number of
reflections will occur just before and just after the first reflection, in addition to the
remaining reflections heard after the first reflection. Thus, the reverb sounds more
Diffusion determines the “thickness” of the reverb sound by adding more reflections
to the reverb’s decay. With lower diffusion settings, you may be able to actually hear
the individual echoes that make up the overall reverb sound. With higher diffusion
settings, the echoes increase in number and blend together, washing out the reverb’s
decay. Greater diffusion works better with percussive sounds, whereas less amounts
of diffusion work well with vocals and other sustained sounds.
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Note: The illustration above reflects a Density setting of 0.
Frequency Damping – Low & High
These two parameters allow you to control the equalization of the reverb’s decay
separately for both the low and high frequencies. This means that you have control
over the tonal shape of the Reverb itself, being able to cut the high frequencies if the
effect is too bright, and being able to cut the lows if the effect is too boomy. These
parameters allow you to simulate different surfaces of a room or hall, with softer
surfaces absorbing more high frequencies and smaller rooms having less low
frequencies. Example: If a room has lots of drapes hung, the high frequencies will
decay faster than the lower frequencies.
Reverberation Swirl
This parameter is very useful for smoothing the decay of the reverb when set at a low
value. When set to a high value, it creates a more dramatic detuning effect as the
reverb decays.
Gating is the process which abruptly cuts off the reverb’s decay for a more “choppy”
sound. This effect is very popular on drums because it makes them sound HUGE. It
is achieved by dropping the level of the signal very rapidly after the initial attack
making a short, sharp sound.
In all the Single Configuration reverb effect types and most of the Double and Multi
Chain Configurations which use the Realroom effect type, there are three gating
parameters available. These include: Gate, Hold Time, and Release Time. The Gate
controls the level of the reverb signal after the gate closes, and can be set between 001
and 100%. In other words, if Gate is set to 100%, then no reverb will sound after the
gate turns it off. If Gate is set to 50%, then some reverb signal will still be present
even after the gate turns off the main reverb signal. Alternatively, the Gate parameter
can be set to “OFF” when you do not wish to use the gating effect. The Hold Time
determines how long the gate will be held open before it begins to turn off; this can
be set from 0 to 500 ms. The rate at which the gate closes is determined by the Release
Time, which can be set from 0 to 500 ms.
In the case of the Chorus->Room, Flange->Room and Room->Flange Configurations,
only one parameter is available: Gate. This can be set between 10 and 500 ms, and
controls both the hold and release times of the gate effect. Alternatively, the Gate
parameter can be set to “OFF” when you do not wish to use the gating effect.
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MidiVerb 4 Reference Manual 33
Delay Effects
Delay provides a discrete repetition of a signal. By adding feedback within the effect,
the delayed signal can repeat many times, with each successive decay softer than its
predecessor. Each of the Delay types allow you to adjust their delay time in
milliseconds, however, the BPM Delay effect will display the equivalent musical
tempo in BPM (beats per minute). MidiVerb 4 offers the following types of delay:
Mono Delay
This Single Configuration provides delay of signal up to 1299 ms. The delay time can
be adjusted separately by 100ths, 10ths and 1 ms increments. Feedback is also
available to increase the complexity of the signal. You also have high and low
frequency cutting, which gives you the ability to equalize the effect’s decay. This can
help emulate an old tape-style echo where each succesive echo is darker than the
previous one.
Stereo Delay
This Single Configuration provides two separate delays which can be individually
adjusted for delay time, feedback and high and low cutting. The delay time can be
adjusted separately by 100ths, 10ths and 1 ms increments.
Ping Pong Delay
So called because the output bounces from left to right in stereo with the speed
determined by the delay time. Again, low and high frequency cut is available. The
delay time can be adjusted separately by 100ths, 10ths and 1 ms increments.
MultiTap Delay
This is like having three delays at once. Each of the 3 “taps” have individual delay,
level, panning and feedback controls. By adjusting the delay time of each tap, you
can create sophisticated rhythms.
BPM Mono Delay
This is a mono delay which can have its delay time parameter set to a specific tempo
or BPM (beats per minute) value. This allows you to reference the delay time to the
tempo of the music you are playing, rather than searching for the correct delay time
in milliseconds.
An additional parameter, called Note, is used to determine what beat value your
tempo represents. For example, if you set the note to 4, then you can set the tempo
using quarter-note beats to establish delay time. If instead you set the Note to 4t, the
same delay tempo setting will play faster because it is simulating quarter-note
triplets in relation to the selected tempo. You can also choose dotted-note values,
such as 4d or 8d for different rhythms relative to the selected tempo.
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Synchronizing to MIDI Clock
It is possible to control the delay time of the BPM Mono Delay effect from an external
MIDI clock source, such as a MIDI sequencer or drum machine. Any device which
can output MIDI clock can be used to control this Configuration’s delay time.
If the “Tempo” parameter is turned all the way down, below 000, the value in the
display will read “EcL”, which means “external clock”. The delay time will now be
controlled by the MIDI clock signal received at the [MIDI IN] port coming from an
external source. If the MIDI clock’s tempo changes, the MidiVerb 4 will chase it. If the
MIDI clock signal is discontinued, the delay time will remain set to the last tempo
which the MIDI clock had been running at.
The Note parameter determines what note value the MidiVerb 4 should synchronize
to. For example, if you set the Note value to 4, then you can synchronize to the
quarter-note beats of the incoming MIDI clock. If instead you set the Note value to 8t,
you can synchronize to eighth-note triplets relative to the incoming MIDI clock
signal. You can also set the Not value to a dotted-note variation, such as *, which lets
you synchronize to the dotted-eighth-note beats relative to the incoming MIDI clock
signal. For more information about using MIDI with the MidiVerb 4, see Chapter 6.
Delay & DLY
These effects are mono, less processor-intensive versions of the Stereo Delay effect,
used in the Multi Chain Configurations Delay->Realroom, Chorus->Dly->Room and
Flange->Dly->Room; the Double Configuration Realroom+Delay; and the Dual Mono
Configurations Delay:Delay, Chorus:Delay and Flange:Delay. They provide only high
frequency cutting ability with no control over the low frequencies.
Setting Delay Time Using Tap Tempo
You can adjust the delay time using a technique called “tap tempo”. By tapping the
button which corresponds to the Tap parameter, you can have the MidiVerb 4 follow
your tapping and adjust its delay time to match the tempo you are using. If the
Footswitch parameter (UTILity mode) is set to Control, you can tap your delay time
by repeatedly pressing down on the footswitch.
You can also adjust the delay time using tap tempo from the audio source being
routed to the MidiVerb 4’s input(s). This can be done in two ways:
• Hold the button which corresponds to the Tap parameter; or
• Hold down the footswitch (if the Footswitch parameter is set to the Control
While using either of these methods, feed signal to the MidiVerb 4. This could be
done by hitting a drum, plucking notes on a guitar or keyboard, or by singing some
“doot doots” into a microphone (depending on what is connected). Note: When the
Footswitch parameter is set to the Control function, you can control tap tempo as
described above while in either Program mode ([PROG] button lit) or Edit mode
([EDIT/PAGE] button lit), unlike when using the front panel for tap tempo which
requires that you be in Edit mode. For more information on connecting a footswitch
and selecting the Footswitch parameter’s function, see Chapter 2.
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MidiVerb 4 Reference Manual 35
Pitch Effects
The Pitch effects alter the pitch of a signal in various ways to produce “layered”
timbres that are more complex than the original signal. Although some of these
effects can sound similar to one another depending on the parameter settings, each is
achieved differently and can be quite dramatic under the right circumstances. Pitch
effects are achieved by splitting the signal into at least two parts, effecting the pitch
of one of the parts, then mixing them back together. This eventual mixing is essential
since the overall sound of the effect is achieved by the actual difference between the
dry, uneffected signal and the effects signal. The various types of Pitch change are:
Stereo Chorus
The Chorus effect is achieved by splitting the signal into three parts with a dry signal
and a separate Detuning section for both left and right channels. When the left
channel is detuned sharp, the right is detuned flat, and vice versa. The detuning is
further effected by being modulated by an LFO (low frequency oscillator) which
causes the detuning to vary. Many variables are available in this scheme: the
Predelay can be varied, the LFO depth can be varied, the LFO speed can be varied,
and a portion of the detuned signal can be fed back to the input to increase the effect.
Finally, the waveform shape of the LFO can be changed from a smooth sinewave, to
a more abrupt squarewave to make the pitch detuning more pronounced.
Quad Chorus
Quad Chorus modulates four delayed signals, each with its phase offset by 90°. Each
of the four signals has a separate Predelay variable, allowing you to change the
“rhythm” of the phasing.
This is a mono, less processor-intensive version of the Stereo Chorus effect, used in
the Multi Chain Configurations Chorus->Realroom and Chorus->Dly->Room, the
Double Configuration Realroom+Chorus, and the Dual Mono Configurations
Chorus:Chorus and Chorus:Delay.
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Stereo Flange
First used in the 1960s, “flanging” was achieved by the use of two tape recorders that
would record and play back the same program in synchronization. By slowing down
one tape machine, and then letting it catch up with the other, different phase
cancellations would occur at different frequencies. Since the slowing down of the
tape machines was done by hand pressure against the flanges of the tape supply
reels, the term “flanging” came into being.
Flanging is similar to chorusing , but modulates the delayed signal over a much
shorter delay range (typically 0-12 ms). This produces a “jet airplane”-like sound.
The flange modulation sweep can be triggered by the audio input (either the left or
right input, or both), in order to sync up with the rhythm of your playing. You can
adjust the attack and release threshold of this audio triggering function.
In the case of the Stereo Flange, the signal is split into three parts with a dry signal
and a separate Delay section for both left and right channels with one channel
flanging up while the other channel flanges down. Once again, this causes the effect
to become more pronounced and dramatic.
When flanging was done using two tape machines, it was possible for one to be
behind the other, catch up and then go past the other. This is called passing “through
zero”. The “zero” point is when both signals were in perfect synchronization. Since
the MidiVerb 4 is digitally simulating the flanging effect, it normally cannot provide
the through zero effect. Instead, it delays the effected signal to a point, then brings it
back to the zero point, and repeats this over and over. The “Thru0” parameter found
in the MidiVerb 4’s flanging effects lets you create the appearance of the effected
signal passing through the zero point. It does this by actually delaying the uneffected
signal by as mush as 12 milliseconds (an amount virtually undetectable to the human
ear). This allows the wet signal to move “behind” the dry signal as it cycles.
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MidiVerb 4 Reference Manual 37
This is a mono, less processor intensive version of the Stereo Flange, used in the
Multi Chain Configurations Flange->Realroom, Realroom->Flange and Flange->Dly-
>Room; the Double Configuration Realroom+Flange; and the Dual Mono
Configurations Flange:Flange and Flange:Delay. The effect of mono flanging is
achieved by splitting and slightly delaying one part of the signal, then varying the
time delay, with an LFO. The delayed signal is then mixed back with the original
sound to produce the “swishing” or “tunneling” sound.
With the Lezlie effect (found in the Lezlie->Room Configuration), the pitch change
block becomes a rotating speaker simulator. This effect was extremely popular
during the 1960’s and was achieved by mechanically rotating the speakers to produce
complex timbral changes. The Lezlie speaker system is most often used with rock
organs, but is occasionally used for guitar amplification as well. Parameters include:
Motor on/off, Speed, which can be slow or fast; and High Rotor Level, which lets
you attenuate the volume of the high frequencies. When switching the Lezlie effect
on and off, or when changing the speed between fast and slow, the effect will ramp
rather than change abruptly, just as a true Lezlie speaker system would do. By
raising the High Rotor Level, you can really make this effect scream. Tip: Try
modulating the Motor or Speed with aftertouch.
Stereo Pitch Shifter
The Pitch Shifter effect transposes the pitch of the incoming signal by a fixed amount.
It is useful for creating parallel harmonies, detuning, chorusing, and special effects.
The Semi parameter shifts the pitch in increments of one half step, with a range of up
or down one octave. The Fine parameter detunes the signal in very fine increments,
with a range of up or down one half step. Also available are Delay and Feedback
parameters. The Delay parameter delays the shifted signal up to 250 ms, or can be
used with the Feedback parameter to produce decaying arpeggio effects. There are
also Low Cut and High Cut filters in the feedback loop which can be used to alter the
timbre of the sound as it repeats. The Stereo Pitch Shift configuration provides two
discrete pitch shifters, each with their own Pan and Level control.
This is a less processor-intensive version of the Pitch Shifter effect, used in the Multi
Chain Configuration Pitch:Delay, and the Dual Mono Configuration Pitch:Pitch.
Auto Pan
The Auto Pan effect alternates the loudness of the signal in opposite channels at a
definable rate. Low and high frequency cutting is available, and (like the flange
effects) can be triggered by the input signal (either the left or right input, or both).
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