Tag: feedback

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Using the Hypno 4: Feedback Modes / Feedback Modulation Mode

To turn feedback on, you have to use the master gain setting in performance mode. Putting that gain in the center position (12 o’clock) effectively turns the image off. Turning the knob to the right adds positive gain, while turning it to the left adds negative gain. When you move past the center point (3 o’clock for positive gain and 9 o’clock for negative gain), you move beyond 100% gain, which introduces feedback. Pressing the center button (B) in performance mode allows the user to toggle between five different feedback modes. Each feedback mode is associated with a different LED color.

ColorFeedback Mode
RedRegular
Green Hyper Digital
YellowEdgy
TealStable Glitch
PinkInverted Stable

A silent video demonstration of the five feedback modes in Hypno.

You can then also adjust various feedback settings by holding down the center button (B), and adjusting the various silders and dials on the Hypno. I call this Feedback Modulation Mode. Moving the dial on the left (A), adjusts the rotation of the feedback. putting the dial to the left of center causes the rotation to move to the left, while moving it to the right of center causes the rotation to move to the right. Moving dial B adjusts the X offset of the feedback, with the center position being no offset. Thus, moving the dial to the left of center causes the feedback to move to the left, and vice versa. Moving dial C adjusts the Y offset of the feedback, with the center position corresponding to no offset, so turning the knob to the left moves the feedback down, while moving the knob to the right moves the feedback up. The dial on the right (D) adds modulation to the rotation of the feedback, with the center position being no modulation. Thus, moving the knob to the left of center causes the feedback to rotate counter clockwise, while moving it to the right of center causes it to rotate clockwise.

The upper two of the center knobs (dial E) zooms the feedback, with the center position corresponding to a 1:1 ratio. Moving the knob to the left zooms in, while moving it to the right zooms out. The lower of the two center knobs (dial F) creates a hue shift for the edges of the shapes. Because this is related to feedback, this can introduce a gradient effect. The two sliders adjust the amount of feedback that is sent back into the gain of the corresponding shape. Thus, slider A affects the gain of shape A, while slider B affects the gain of shape B. In order to do this, we need to first turn on cross modulation by pressing the button for the current oscillator (button A for oscillator A and button C for oscillator B). While holding this button, tapping the button for the other oscillator will toggle cross modulation on or off. This will be indicated by a green (on) or red (off) LED.

A silent video of most of the feedback modulation options in Regular Feedback mode..

A bit of experimentation is called for here in order to get an idea of what the possibilities are. That being said, making numerous setting changes in feedback modulation mode can be difficult to to undo, so, you might find it useful to restart the Hypno between trying out each of the Feedback modes.

Here is the Sleepy Circuits quick guide for Feedback Mode . . .


video by Sleepy Circuits

Likewise, here’s the Sleepy Circuits quick guide for Feedback Controls . . .


video by Sleepy Circuits

Here we find a quick guide by Sleepy Circuits which describes how to use button patching for cross modulation . . .


video by Sleepy Circuits

Using the Hypno 5: Using Input Shapes

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Feedback in FM Synthesis

FM Synthesis can be difficult to understand. Those of us who spent time programming a Yamaha DX7, the leading FM synthesizer of the 1980s, also know how confusing it can be to program. Fortunately for those who are nostalgic for classic synthesizers of the 1980s Digital Suburban develed Dexed, a DX7 emulator.

The good news is that Dexed works just like a DX7, allowing you to port over classic patches. The bad news is that Dexed works just like a DX7, in that it can still be confusing and awkward to program. However, the better you understand FM synthesis, the better equipped you’ll be to tackle Dexed.

In this post we’ll investigate feedback, which in FM synthesis is when some of the output an operator is fed back to modulate itself. In a DX7, there are eight levels of feedback available (0-7 inclusive). No feedback is present at level 0, while at level 7 there is (presumably) 100% feedback.

I tested feedback in Dexed by using algorithm 32, which is the only algorithm in which a carrier modulates itself. I turned off all the operators except for operator six, which is set at full volume, and at a ratio of 1.00 (the first harmonic). Each pitch is at A4 (440Hz) with full velocity.

It is interesting to see and hear the results of the test. Predictably at feedback level 0 a simple sine wave results. At feedback level 1 the second harmonic starts to appear at less than 1/4 the strength of the first harmonic. At feedback level 2, this second harmonic somewhat stronger (at approximately 1/4 strength). At feedback level 3, the first four harmonics are present with the strength of each being about 1/3 the strength of the previous harmonic. At feedback level 4, the harmonic spectrum of the first eight partials of a sawtooth wave become recognizable. We get the first 18 partials at level 5. At level 6 we get what could be called a hyper sawtooth wave, with a very strong peak at partial 34, with lesser peaks running up from partials 26 through 46. Finally, at level 7 we get a white noise spectrum with added strong partials at the first two harmonics.

This analysis bears out when looking at the resulting waveforms in Audacity. We start with a pure sine tone, and with each increase of the level we start to see the sine wave lean to the left a bit. By feedback level 3, a smoothed sawtooth wave is clearly visible. At level 5 we see a pretty close approximation of a sawtooth wave. The waveform at level 6 appears to be 34 periods of sawtooth waves shaped into sawtooth wave type shape at the frequency of the first harmonic. Furthermore, we get a significant amount of positive side DC offset in the waveform, leading to some distortion (we had actually gotten some DC offset at level 5 as well). The waveform at level 7 has a clear profile of white noise, though it seems to have occasional fragments of a noisey square wave. Interesting enough we also get a small amount of negative side DC offset.

Ultimately, what we learn is that feedback shapes an oscillator’s sine wave into a sawtooth wave, peaking at level 5, moving into a hyper sawtooth wave at level 6, and becoming largely white noise at level 7.