MODX: Rotary speaker (part 5)

Posted on June 28, 2023 by pj

It should go without saying — the Leslie rotary speaker sound is critical to getting a good drawbar organ sound.

The Montage/MODX and Genos/PSR product lines have two rotary speaker effects in common:

     MODX effect name  Genos effect name 
     ----------------  ----------------- 
     Rotary Speaker 1  ROTARY SPEAKER 1 
     Rotary Speaker 2  REAL ROTARY

Yamaha’s naming scheme often makes it difficult to match up algorithms across product lines. Rest assured, however, the algorithms (and code) are the same. If you need to double check yourself, simply match up the effect parameters as listed in the Data List PDFs.

It’s like the engineers deliberately chose bad, meaningless variable names. Throw preset names on top of the algorithm (effect type) names and things get really confusing!

Rest assured, a lot of the information discussed in this post can be applied to Yamaha synthesizer and arranger products alike.

The real thing: mechanical

Ain’t nothin’ like the real thing, baby. A real Leslie speaker moves air and throws it around in a 3D space. A “2D” stereo simulation will never do. Further, rotary speaker simulators model a mic’ed up speaker putting strong energy surges into the left and right channels.

We all know that a Leslie speaker, like the 122, has a rotating horn and rotor. Yamaha sometimes refer to the rotor as a “woofer”, so keep that in mind when reading through effect parameters!

The horn and rotor each have a motor. The motors have two speeds when turning: slow and fast. A pulley and belt system transfers rotation from a motor to the horn or rotor. The horn motor has three different sized-pulleys: small, middle, and large. The belt is usually around the middle pulley, AKA the factory setting. If the belt is around the small pulley, the rotor turns slower. Put the belt around the large pulley and the rotor turns faster (relative to the factory setting, of course.)

The nominal, factory rotary speeds are:

    Slow / "Chorale" in Leslie terminology 
        Horn           50 RPM   0.83 Hz 
        Woofer/Rotor   40 RPM   0.67 Hz 
    Fast / "Tremolo" 
        Horn           400 RPM  6.67 Hz 
        Woofer/Rotor   340 RPM  5.67 Hz

You should keep these speeds in mind when tweaking parameters, if you want authenticity. Please note that the rotor turns more slowly than the horn.

I gave the nominal speeds in both rotations per minute (RPM) and cycles per second (Hertz). Some algorithms need RPM and other algorithms need Hertz. Here are conversion formulas:

    RPM = Hertz * 60 
    Hertz = RPM / 60

The pulley and belt system causes even more fun. The belt is flexible and slips around the pulley. Belt tension and wear determine slip. Tension (slip) has a greater effect on acceleration (change from slow to fast) than deacceleration (change from fast to slow). If you want authenticity, acceleration time should be shorter than deacceleration. In other words, the pick-up rate is higher than the slow-down rate.

The real thing: electronics

The Leslie 122 tweeter and woofer are driven by a three tube power amplifier through a cross-over network. The classic Leslie crossover frequency is 800 Hertz. The crossover filter is not super steep and there is definite frequency bleed beyond the crossover frequency.

The power amp consists of a 12AU7A tube driving dual 6550 power tubes. The 12AU7A belongs to a family of nine pin, twin triode tubes. The chief difference between family members is the gain factor. The 12AU7A has a gain factor of 20 while the more powerful 12AX7 — the most familiar member of the family — has a gain factor of 100.

The power amp has a gain knob. At about 70%, the power amp starts to distort. Oh, never, ever go past 70%. Ever. 🙂

The sims

With that background in mind, let’s take a look at the Yamaha MODX rotary speaker effect algorithms.

Historically, “Rotary Speaker 1” came first. The following table summarizes the Genos parameter values for the “Dual Rotary Speaker Bright” and “Dual Rotary Speaker Warm” presets:

     # Parameter             Bright    Warm 
    -- --------------------  --------  ---------------- 
     1 Woofer Speed Slow     40.2rpm   40.2rpm   0.67Hz 
     2 Horn Speed Slow       45.6rpm   45.6rpm   0.76Hz 
     3 Woofer Speed Fast     383.4rpm  363.6rpm  6.06Hz 
     4 Horn Speed Fast       403.8rpm  403.8rpm  6.73Hz 
     5 Slow-Fast Time Woofer 39        45 
     6 Slow-Fast Time Horn   7         7 
     7 Drive Low             35        31 
     8 Drive High            37        36 
     9 Low/High Balance      L<H4      L13>H 
    10 
    11 EQ Low Frequency      100Hz     100Hz 
    12 EQ Low Gain           +8dB      +8dB 
    13 EQ High Frequency     1.0kHz    1.0kHz 
    14 EQ High Gain          -3dB      -4dB 
    15 Mic L-R Angle         177deg    177deg 
    16 Speed Control         Slow      Slow

Feel free to borrow the Genos settings for MODX (and vice versa).

The horn and woofer speeds are ballpark with respect to the factory settings. If there is one major complaint with this algorithm, it’s the relatively weak drive effect. Increasing drive does not add distortion. On MODX, be prepared to couple “Rotary Speaker 1” with an amp simulator (e.g., STEREO SMALL or MULTI FX).

Obviously, there are a lot of parameters to tweak: microphone angle, equalization, rotor and horn balance (low/high balance). Imagine yourself as a studio engineer mic’ing up a real Leslie.

Just for grins, the following table summarizes rotary speaker parameters for four MODX presets:

     # Parameter             Basic     Horn Mic  Light     Heavy RTR 
    -- --------------------  --------  --------  --------  --------- 
     1 Rotor Speed Slow      0.88Hz    0.80Hz    0.88Hz    1.01Hz 
     2 Horn Speed Slow       1.30Hz    0.72Hz    1.30Hz    0.93Hz 
     3 Rotor Speed           6.06Hz    6.06Hz    6.06Hz    6.06Hz 
     4 Horn Speed Fast       7.07Hz    6.73Hz    7.07Hz    6.73Hz 
     5 Slow-Fast Time Rotor  40        40        40        64 
     6 Slow-Fast Time Horn   13        12        13        33 
     7 Drive Rotor           52        37        26        28 
     8 Drive Horn            31        29        21        22 
     9 Rotor/Horn Balance    RH 
    10 
    11 EQ Low Frequency     1.0KHz     1.0KHz    1.0KHz    1.0KHz 
    12 EQ Low Gain          0.0db      -1db      0.0db     0.0db 
    13 EQ High Frequency    2.0KHz     2.0KHz    1.0KHz    2.0KHz 
    14 EQ High Gain         0.0db      +1db      0.0db     1.0db 
    15 Mic L-R Angle        150deg     177deg    180deg    30deg 
    16 Speed Control        Slow       Slow      Slow      Slow

Enough starting points yet? Please don’t be afraid to tweak, listen and evaluate. It’s only bits and if you don’t like what you’re hearing, then throw the bits way away. Ever wonder why people spend so much time in the studio? That’s why!

The MODX “Rotary Speaker 2” algorithm is the newer algorithm. It first appeared in Montage and Genos, and it’s been trickling down to mid- and low-range Yamaha products. In Genos-land, it’s known as “REAL ROTARY”. This algorithm provides control over both acceleration and deacceleration times and drive level/tone.

Here are settings from Genos for three drawbar organ voices:

     # Parameter            Jazz      Gospel    Rock 
    -- -------------------  --------  --------  -------- 
     1 Speed Control        Slow      Fast      Fast 
     2 Drive                2.0       4.0       10.0 
     3 Tone                 8.2       10.0      10.0 
     4 Low/High Balance     L<H10     L<H9      L<H9 
     5 Output Level         100       100       100 
     6 Mic L-R Angle        180deg    120deg    120deg 
     7 Input Level          +6dB      +6dB      +6dB 
     8 Modulation Intensity 0         63        63 
     9 
    10 
    11 Slow-Fast Time Horn  1.19      1.13      1.13 
    12 Fast-Slow Time Horn  0.86      0.97      0.97 
    13 Woofer Speed Slow    43.5rpm   43.5rpm   43.5rpm 
    14 Horn Speed Slow      47.3rpm   47.3rpm   47.3rpm 
    15 Woofer Speed Fast    413.8rpm  403.7rpm  413.8rpm 
    16 Horn Speed Fast      474.4rpm  464.3rpm  464.3rpm 
    17 Slow-Fast Time Rotor    ?         ?         ? 
    18 Fast-Slow Time Rotor    ?         ?         ?

Unlike “Rotary Speaker 1”, REAL ROTARY brings overdrive. Turn up the drive to add distortion. Tone sweeps from darker to brighter.

No doubt, you noticed values missing in the last two rows. The Genos user interface supports only 16 effect parameters! [Genos engineers need to fix this limitation.] Your guess is as good as mine — maybe 1.22 and 1.86?

Other blog posts about Yamaha MODX drawbar organ sound design:

Critique: Genos™ drawbar organ

Posted on October 25, 2021 by pj

I like the Korg Module Pro “GospelOrgan” patch, so I tried to create a sound-alike voice on Yamaha Genos. Genos and MODX share the same waveforms and DSP effects, and I may port the result to MODX, too.

The experience recalled my previous misgivings about the rotary speaker simulation and limitations of the Genos DSP effect implementation. I will amplify those comments here.

Mid- to upper-level Yamaha arranger workstation have long had a drawbar organ feature which Yamaha calls “Organ Flutes.” This feature dates back to 1999, appearing in the PSR-9000 keyboard. Although a few details have changed over the years, Yamaha has not substantially overhauled Organ Flutes. It’s time, Yamaha — the world has moved on. I’d love to see the new YC organ technology in Genos. It’s the flagship of the arranger line and YC organs would definitely differentiate Genos from its lower-cost brethren.

Yamaha Organ Flutes main voice editing screen

The main, tweakable organ parameters are:

Nine drawbars
Percussion (first note/each note, length)
Percussion pitch (4′, 2-2/3′, 2′)
Response (onset delay of drawbar and percussion sounds)
Vibrato (on/off, depth, speed)
Rotary speaker speed (slow/fast)
Volume level (1 to 8)
DSP effect (e.g., rotary speaker)

For B-3’ers, the 4′ percussion pitch is the 2nd harmonic setting and the 2-2/3′ percussion pitch is the 3rd harmonic setting. The 2′ pitch supports non-Hammond organs which require it.

Compared with a contemporary clonewheel, one immediately notes a few missing features:

Vibrato only, no chorus
No key click
No rotor noise
No leakage

Overall, the Genos B-3 is super clean and polite — not vintage. MODX (Montage) provides key click, rotor noise (grit) and rotor whistle waveforms. Why does Genos lag behind? Although MODX is AWM2, not modeling, these extra waveforms are better than nothing at all.

The Genos synthesis engine is also AWM2 sample-playback and AWM2 provides the Organ Flutes vibrato. Organ Flutes does not simulate the one-of-a-kind Hammond vibrato/chorus scanner. The Korg Module “Gospel Organ” voice incorporates C-3 chorus and the AMW2 vibrato just doesn’t cut it (head-to-head comparison). I had to substitute Genos’ V-2 setting and move on.

Simplified, graphical rotary speaker interface

If you want to change the rotary speaker type, you need to dive through the effect setting button at the top of the Organ Flutes screen. After selecting the insertion effect, Genos displays a skeuomorphic (graphical) rotary speaker cabinet with a few knobs. In the screenshot above, we get rotary speed, horn and rotor balance, and microphone left/right angle. Like many (most?) rotary speaker simulations, the rotary effect emulates the sound of a mic’d up, stereo recording of a Leslie, not a horn and rotor moving air in a room.

Additional rotary speaker (DSP) parameters are changed by tapping the “Detail” button in the lower right corner. deep-diving reveals a few more deficiencies:

Missing parameters due to a limitation on the number of DSP effect parameters (16 parameters maximum)
Only one insert effect (typically the rotary speaker)
Volume control is post-effect and does not affect overdrive

Here is a little more information about each issue.

At heart, the Genos (PSR, Tyros) sound engine implements the Yamaha XG synthesis and effects architecture. The XG architecture allows up to sixteen (!6) parameters per DSP effect unit. Unfortunately, Yamaha’s DSP engineers are creating effect algorithms (AKA “effect types”) with more than sixteen parameters! The MODX ROTARY SPEAKER 2 algorithm has eighteen (18) parameters. The Genos REAL ROTARY effect type is the same algorithm as MODX. However, only 16 parameters are accessible or stored on Genos. The two missing REAL ROTARY parameters are:

Slow-Fast Time of Rotor
Fast-Slow Time of Rotor

You cannot change these rotor ramp times on Genos, yet, you can change them on MODX.

This issues affects the Genos UNI COMP compressor algorithm (MODX: UNIVERSAL COMPRESSOR DOWN). Dare I mention the inability to specify a side-chain part, too? People are trying to create EDM on arrangers.

The XG architecture allows only one insert effect per part. The Organ Flutes insertion effect is typically a rotary speaker simulator. The MODX effect architecture, on the other hand, allows two insert effects per part. Yamaha synths take advantage of the second insert effect to add overdrive or vintage EQ:

Rotary speaker 1 → Multi FX (Distortion Solo)
Rotary speaker 2 → VCM 501 EQ (Flat)
Amp Simulator 3 (Tube) → VCM 501 (Flat)
Amp Simulator 1 (Stack 2) → Rotary Speaker 1
VCM 501 EQ (Flat) → Rotary Speaker 1

The rotary speaker drive alone is not enough to warm up the basic sound nor is it enough to get a sweet, realistic overdrive with guts. I experimented with the Genos REAL ROTARY effect and got some very squirelly results at high drive levels. The algorithm can be pushed in unexpected, undesirable ways while searching for true funk.

Unlike a real Hammond/Leslie combination, the Genos expression pedal controls post-effect part volume. This is like putting the volume control after the Leslie speaker. A Hammond B-3 pedal controls the level into the Leslie pre-amp. Thus, the pre-amp frequency characteristics and overdrive track the Hammond pedal. The Yamaha YC61 modeling gets this right. Putting the volume pedal before the pre-amp lets the player get clean or dirty in the same way a guitarist uses picking and/or the guitar volume knob to distort or clean up their tone.

If the Genos developers must work around the XG architecture, they should consider a new effect algorithm that combines overdrive with the rotary speaker simulation. The algorithm should allow foot pedal control over the Leslie pre-amp input level. Genos and other PSRs allow wah pedal control, so they obviously know how to achieve this capability within the current architecture.

Time stretching applied to rotary speaker sound

Posted on June 20, 2018 by pj

“Sí, sí, I am very intrigued.”

With Summer NAMM 2018 one week away, I cast the net to see what I can catch. I did a quick sweep of recent patents and came up with a good ‘un.

When folks mention Yamaha, “tonewheel clone” does not immediately come to mind. Other players like Nord, Hammond Suzuki, etc. seem to be ahead in the clone market. So, I was a little surprised to find US Patent 9,899,016 B2, “Musical sound signal generation apparatus that generates sound emulating sound emitting from a rotary speaker.” This patent was issued and assigned to Yamaha on February 20, 2018. It is based on the Japanese patent 2015-171065 issued August 31, 2015.

Yamaha currently use two sample-based methods to generate the basic organ sound:

Playback and mix of waveforms for each individual tone wheel. On Montage and Genos, for example, the musician can adjust the level of each footage using the sliders to mimic drawbars. The generated sound is passed through a rotary speak DSP effect.
Playback of waveforms for “full up” organ registrations with and without the rotary speaker effect “sampled in.” The resulting sound may also be passed through a rotary speaker DSP effect.

In the first case, especially, the overall impression of a genuine B-3 depends upon the quality of the DSP rotary speaker effect. The up-side of the DSP effect is the ability to ramp up and ramp down the rotary speaker speed. So far, reaction to Yamaha’s rotary speaker effects has been mixed.

In the second case, one is not likely to put the sound through a rotary DSP effect — the swirling mass would just not be realistic. The “sampled in” approach can sound more realistic than the rotary DSP effect, but it has two major drawbacks:

The rotary speaker speed cannot ramp up and down between slow and fast rotation.
Sample playback does not align (synchronize) the rotary speaker position, so some noted are “rotating” faster than others and the true spatial characteristics of the horn and rotor are lost.

The second drawback is perhaps the worst of the two since it introduces audible artifacts which are not part of the true rotary speaker sound.

The method in the patent is a different take on sample-based synthesis of tone wheel sound which seeks to eliminate these problems. The notes are sampled for each tone wheel footage after a real world rotary speaker rotating at a particular rate. In each case, wavfeorms are sampled and saved for various rotational angles of the rotary speaker. Thus, the rotary speaker effect is “sampled in.”

Let’s quote from the patent:

Also, the electronic musical instrument has a time stretching function. The time stretching function is a function of changing the length of a sound while maintaining the pitch and formant of the sound. In other words, with the time stretching function, it is possible to extend and shorten a sound in a time axis direction, or in other words, it is possible to change only the reproduction speed (speed with which time advances) of the musical sound signal. The electronic musical instrument uses the time stretching function to extend and shorten each piece of waveform data in the time axis direction by the same extension and shortening rates.

Time stretching is applied to each of the tone wheel samples during playback. Thanks to time stretching, the instrument can reproduce the SLOW and FAST sound, and everything in between when the rotation speed ramps up or down. “A known pitch synchronous overlap and add method is used to achieve the time stretching function.”

The rest of the method — and it is both exhaustive and exhausting! — deals with the synchronization of the waveforms during playback, that is, the alignment of each waveform in accordance with the current virtual position (rotational angle) of the rotary speaker. Throw in separate treatment of the horn and rotor, stereo channels, etc.

The end result is a unique sample-based method that eliminates the problems of “sampled in” rotary speaker effects. I wish that patents came with audio demo files as it would be a treat to hear the method in action and to judge with one’s own ears. Maybe someday in a product?

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