Cemu

Guitar Amp Phys Modeller VST-Plugin CEMU

ФРМИ2.653.020 Д28

Content 1

Introduction_________________________________________________________________ 4

2

Common block diagram _______________________________________________________ 5

3

Channel 2 Band-Pass Filter ____________________________________________________ 5

4

5

3.1

Minimum Frequency (Ch2Fmin) __________________________________________________ 5

3.2

Maximum Frequency (Ch2Fmax) _________________________________________________ 5

Phase-controlled Auto Wah’s___________________________________________________ 6 4.1

Channel 1 Wah Gain (Ch1Wah Gain)______________________________________________ 6

4.2

Channel 2 Wah Gain (Ch2Wah Gain)______________________________________________ 6

4.3

Channel 1 Wah autotune rate (Ch1Wah Rate)_______________________________________ 6

4.4

Channel 2 Wah autotune rate (Ch2Wah Rate)_______________________________________ 6

Compressors ________________________________________________________________ 6 5.1

Treshold ______________________________________________________________________ 6

5.2

Release _______________________________________________________________________ 6

5.3

Input highpass filter frequency (In HiPass ) _________________________________________ 6

5.4

Input lowpass filter frequency (In LowPass ) ________________________________________ 6

5.5

Output Gain-Controlled Lowpass Filter Minimum Frequency (Wah F min) ______________ 6

5.6

Output Gain-Controlled Lowpass Filter Maximum Frequency (Wah F max) _____________ 6

5.7

Assumed Peak/RMS ratio (Peak/RMS) _____________________________________________ 6

5.8

Look-ahead time (Pre-Fade) _____________________________________________________ 6

5.9

Transfer characteristic mode (Cmpr Mode) _________________________________________ 6

5.10

Output Volume (Out Vol) ______________________________________________________ 7

6

Preamps ____________________________________________________________________ 7

7

Power Amp _________________________________________________________________ 7

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7.1

Assymetry of power tubes (Tube asymm) ___________________________________________ 8

7.2

Input resistance of transformer (Xfrm R1)__________________________________________ 8

7.3

Input capacitance of transformer (Xfrm R1) ________________________________________ 8

7.4

Primary wound inductance of transformer (Xfrm L1) ________________________________ 8

7.5

Ratio of transformer (Xfrm ratio) _________________________________________________ 8

7.6

Output resistance of transformer + resistance of speake r( or both) (Xfrm R2+Rspk) ______ 8

7.7

Transformer B-H hysteresis loop size (Xfrm hyst size) ________________________________ 8

7.8

Transformer B-H hysteresis loop amount (Xfrm hyst amnt) ___________________________ 8

7.9

Transformer B-H saturation amount (Xfrm ovld amnt) _______________________________ 8

7.10

Type of power tubes. (Pow TubeType) ___________________________________________ 8

7.11

Presence (Presence)___________________________________________________________ 8

7.12

Low corner frequency of highpass RC-chain in feedback (Presence HPF) ______________ 8

Speakers____________________________________________________________________ 8 2

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8.1

Speaker(1st or both) inductance (Spkr L) ___________________________________________ 8

8.2

Speaker(1st or 2nd ) center resonant frequency (Spk Fres) _____________________________ 8

8.3

Speaker(1st or 2nd ) center mechanical resonance quality (Spk Q) _______________________ 8

8.4

Speaker(1st or 2nd ) microphone EMF coefficient (Spk Mic EMF)_______________________ 8

8.5

Speaker(1st or 2nd ) center’s mass to surface’s mass ratio (Spk mCntr / mSrfc) ____________ 8

8.6

Coil returning mechanical force by coil position hysteresis loop size(Spk Hst Size) _________ 9

8.7

Coil returning mechanical force by coil position hysteresis amount (Spk Hst Amnt) _______ 9

8.8

Speaker surface radial wave 2nd order non-linearity coefficient (Spk 2HD)_______________ 9

8.9 Speaker surface radial wave 3rd order non-linearity coefficient relative to 2nd order (Spk 3HD / 2HD)______________________________________________________________________________ 9

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8.10

Influence of speaker-mic distance change by speaker moving coefficient (Doppler) ______ 9

8.11

Speaker(1st or 2nd ) virtual re-sizing coefficient (Spkr ReSize) ________________________ 9

Auto-Equalizer ______________________________________________________________ 9 9.1

Limit of Auto-Equalizer boost at any frequency (AutoEQ Range) ______________________ 9

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1

Introduction

Guitar Amp Phys Modeller CEMU1 VST-plugin includes scheme level modelling of essential tube parts of amp: preamp, poweramp and speaker&mic as well as compressor and auto-wah at input, which are not the clones of analogue parts thus using advantages of clear discrete technology such as look-ahead.

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2 Common block diagram CEMU contains of: - implicit input 2-way splitter. - Channel 2 Band-Pass Filter, generally used to make Channel 2 work with higher frequencies of input. - 2 identical Compressors (1&2). Alhough Compressors have adjustable parameters, which can make it work different way. Lowpass filters included of each compressor are used to remove excessive-high frequency noise from input and to limit Channel 1 band usualy at the same frequency as low-corner frequency of Band-Pass Filter of Channel 2 to make 2band compression. - 2 identical Preamps. Alhough Preampss have adjustable parameters, which can make it work different way. - Power Amp ( the only ;) . - 2 speakers of independently choosable type with movable from centre to edge mics.

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3 Channel 2 Band-Pass Filter Channel 2 Bans-Pass Filter is hi-order bandpass filter with adjustable boundaries of pass band.

3.1 Minimum Frequency (Ch2Fmin) Low corner of pass band. 3.2 Maximum Frequency (Ch2Fmax) High corner of pass band.

4 Phase-controlled Auto Wah’s Each channel have implicitly bypassable auto-wah, both of identical scheme. Auto Wah have unity gain far from resonant frequency and gain at resonant frequency equal Channel 1(2)Wah Gain. Thus when gain is set to 0 dB wah is bypassed. Autotuning of wah trying to find maximum or 6

ФРМИ2.653.020 Д28

middle of input signal spectrum. This is done by the fact that the phase of 2nd order bandpass filter is positive at lower than resonant frequencies and negative at higher. Thus it works similar the PLL way. 4.1 Channel 1 Wah Gain (Ch1Wah Gain) Gain at resonant frequency of wah 1. 4.2 Channel 2 Wah Gain (Ch2Wah Gain) Gain at resonant frequency of wah 2. 4.3 Channel 1 Wah autotune rate (Ch1Wah Rate) Speed of wah 1 autotuning. 4.4 Channel 2 Wah autotune rate (Ch2Wah Rate) Speed of wah 2 autotuning.

5 Compressors After auto-wah each channel signal passes to respective compressor, both of identical scheme. Each Compressor have the same parameter set, so here described one ;) 5.1

Treshold

5.2

Release

5.3 Input highpass filter frequency (In HiPass ) Compressor have input highpass filter to cut off DC and unneeded low frequencies. This parameter controls -3dB corner frequency of it. 5.4 Input lowpass filter frequency (In LowPass ) Compressor have input lowpass 4-order filter to cut off unneeded high frequencies. This parameter controls -3dB corner frequency of it. 5.5 Output Gain-Controlled Lowpass Filter Minimum Frequency (Wah F min) Compressor have output gain-controlled lowpass 4-order filter which can be used as levelcontrolled wah or level-controlled hi-freq noise filter. This parameter controls -3dB corner frequency of it when gain of compressor is max (input level is min). 5.6 Output Gain-Controlled Lowpass Filter Maximum Frequency (Wah F max) Compressor have output gain-controlled lowpass 4-order filter which can be used as levelcontrolled wah or level-controlled hi-freq noise filter. This parameter controls -3dB corner frequency of it when gain of compressor is min (input level is max).

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5.7 Assumed Peak/RMS ratio (Peak/RMS) Compressor works in switchable peak-hold/RMS mode. When input signal overcomes RMS value of detector multiplied by assumed Peak/RMS ratio compressor switches to peak-hold mode for the time, equal look-ahead time – to let look-ahead-gain-smooth filter reach respective to peak level value. After peak-hold time expired RMS detector set to value equal last peak level divided by assumed Peak/RMS ratio and compressor returns back to RMS mode. Thus if this value set too low compressor will switch to frequently but if too high – mean level will be lowered. 5.8 Look-ahead time (Pre-Fade) One of evident advantages of digital compressor is ability to adjust gain prior to peak, also called look-ahead. The bigger look-ahead time the smoother gain curve can be, but the higher delay introduced. 5.9 Transfer characteristic mode (Cmpr Mode) Compressor may work in two modes of dependency of output level on input level: Soft and Hard. In Soft Mode the input-output graph turns to constant around treshold smoother but in price of lowering levels of pre-treshold input levels. 5.10 Output Volume (Out Vol)

6 Preamps C CEMU have unique feature – 2 preamps. Both are of identical scheme:

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All marked at above scheme parts are adjustable in wide range independently for each preamp. If preamp 1 only used it works in 3-tube mode, when both – then in 2-tube and diode pair mode. When only preamp 1 used outputs of both wah’s are mixed at input of it. When coth preamps are used – outputs of it are mixed before feed the power amp.

7 Power Amp Power Amp model calculates interaction of output tubes, transformer and speaker. 2 speakers may be turned or the only 1st. Generalized scheme of power amp with speaker is next:

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7.1

Assymetry of power tubes (Tube asymm)

2nd order assymetry of output tubes.

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ФРМИ2.653.020 Д28

7.2

Input resistance of transformer (Xfrm R1)

7.3

Input capacitance of transformer (Xfrm R1)

7.4

Primary wound inductance of transformer (Xfrm L1)

7.5

Ratio of transformer (Xfrm ratio)

7.6

Output resistance of transformer + resistance of speake r( or both) (Xfrm R2+Rspk)

7.7 Transformer B-H hysteresis loop size (Xfrm hyst size) Model of transformer includes hysteresis. This is the size of ti’s loop in some relative measure. 7.8 Transformer B-H hysteresis loop amount (Xfrm hyst amnt) Ratio of dB/dH after H change direction changed.

7.9

Transformer B-H saturation amount (Xfrm ovld amnt)

7.10 Type of power tubes. (Pow TubeType) Triod/Penthod. 7.11 Presence (Presence) As well known presence parameter of tube power guitar amp is nothing else but absence of feedback. Maximum vakue means nearly no feedback at all. 7.12 Low corner frequency of highpass RC-chain in feedback (Presence HPF) The higher vakue the more high frequencies only are included in poweramp feedback.

8 Speakers Speakers in CEMU are simulated in true complex way. Nonlinear (3rd order) Finite-Difference scheme is used to physically model radial wave propagation on speaker surface as well as speaker center elasticity and EMF, caused by coil movement in magnetic field as in dynamic mics . Moreover: propertiary math used to calculate wave parameters of speaker surface which for given discrete-wave nodes count most closely (in some mean) approximate destinative (original) amplitude-frequency response (in linear case). Also each speaker can be virtually re-sized independent of another. Type of each speaker can be select independently too. As well interspeaker delay and mix can be adjusted.

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ФРМИ2.653.020 Д28

8.1

Speaker(1st or both) inductance (Spkr L)

8.2

Speaker(1st or 2nd ) center resonant frequency (Spk Fres)

8.3

Speaker(1st or 2nd ) center mechanical resonance quality (Spk Q)

8.4

Speaker(1st or 2nd ) microphone EMF coefficient (Spk Mic EMF)

8.5 Speaker(1st or 2nd ) center’s mass to surface’s mass ratio (Spk mCntr / mSrfc) Higher values effectively increases influence of surface wave behavior to movement of coil and consequently to mic EMF of speaker. 8.6

Coil returning mechanical force by coil position hysteresis loop size(Spk Hst Size)

8.7

Coil returning mechanical force by coil position hysteresis amount (Spk Hst Amnt)

8.8 Speaker surface radial wave 2nd order non-linearity coefficient (Spk 2HD) Higher values make sound more sharp and dynamic but excessive values can lead to dirty sound. 8.9

Speaker surface radial wave 3rd order non-linearity coefficient relative to 2nd order (Spk 3HD / 2HD)

8.10 Influence of speaker-mic distance change by speaker moving coefficient (Doppler) As for speaker non-linearity higher values make sound more sharp and dynamic but excessive values can lead to dirty sound. 8.11 Speaker(1st or 2nd ) virtual re-sizing coefficient (Spkr ReSize) Each speaker independently can be resized with respective change of sound.

9 Auto-Equalizer Used to compensate unneeded resonances of user’s guitar to achieve required spectrum. Have “learn” mode. While in this mode Auto-Equalizer tuned to compensate spectral inequalities at point of speaker current. Therefore it doesn’t equalizing spectrum coloring made by speaker. 9.1 Limit of Auto-Equalizer boost at any frequency (AutoEQ Range) As soon as real physical laws complained signal spectrum must decrease after some frequency and/or input signal may have notches, Auto Equalizer shouldn’t be allowed to boost any frequency infinitely. Thus this is the limit of boost ever.

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