Gamma Jumpiness

Trying to get a smooth gamma light flicker is a challenge. I think a lot of it is inherent to the Kasina. Anybody have any tips or hacks? I tried different waveforms, intensities, AS, SS, nothing seems to work.

What frequency are you shooting for? For my Gamma sessions I usually do 40hz. It doesn’t seem to flicker.

40 Hz. Sharp duty cycles work better for these fast frequencies. Whatever the waveform, duty cycle, or color you can see some jumpiness, kind of odd fluctuation in intensity. Robert explained a while back something about that the Kasina has to go into alternating flashing or something like that to get the faster frequencies.

This is a bit of speculation on my part but based on what I’ve learned so far:

The filters of AS and SS need a “window” of audio samples to be able to extract the amplitude of the various high frequency tones and extract it to the various LED channel output levels. This is true of most filters in general, and in the case of things that like Fast Fourier Transform the size of this window/buffer of samples is a trade off between accuracy and output latency.

With the Kasina this is based on the sample rate of the audio. Robert said he wasn’t sure but it was something like 128 or 256 samples. So to determine the maximum theoretical “visual frame rate” of the Kasina, you divide the sample rate of the audio track by this buffer size. Here are a few examples:

48000 / 256 = 187.5 fps

48000 / 128 = 375 fps

44100 / 256 = ~172.3 fps

44100 / 128 = ~344.5 fps

So we don’t know exactly what the frame rates are but they are somewhere in that ballpark.

On top of that the LED signals of the glasses also use interlaced frames. That is, at some unknown rate (but fast enough to trick our eyes) only one eye is powered at a time in a 50/50 cycle. That’s how they control 6 channels of color (left RGB / right RGB) with only 4 conductors on the headphone jack style TRRS cable. It’s a pretty awesome hardware hack, but it means the LEDs of both eyes are never on at the same time. I never learned what rate at which the eyes alternate on/off, just that they do. And on top of that the Kasina is likely using a duty cycle of pulse width modulation to control output intensity of each LED, which again has a different (and unknown to me) rate of cycling on/off.

Now why do I mention all of this? Well, what we have is a lot of independent on/off cycles of the system, as well as a maximum frame rate that is certainly less than 400 fps. As the visual modulation rate of the entrainment signal increases, it becomes harder and harder to perfectly reproduce them without visual glitches such as “dropped frames”. So the visual output you experience is a combinatory factor of all of these different rates interfering with each other mathematically in time. Sometimes the exact output and frame will line up perfectly, sometimes it will not. It also depends on all of the phases of these signals too.

All that said, the explanation may be even more simple. Without the glasses or your eyes in motion, you are dealing with persistence of vision (POV) which is a biological issue with visual processing in the brain. As the frame rate increases, the frames begin to “blur” together, and you stop being able to perceive them as individual frames in time. Joe you are correct that smaller pulse widths can allow you retain perceived flicker at higher frame rates, but the other problem with this, especially as you go faster and faster, is that you will also perceive dimmer output since the LEDs are on less and less in time, and the eye perceived brightness as the average output power of the signal in time (RMS).

For me, when I try 40 Hz visual, even pulse width, I just perceive it as a mostly solid output that just happens to shimmer a bit. I think some of this is due to POV and is expected, and some of it is due to all the other issues I outlined above. As all of the various integer multiples of the various rates and cycles of the system combine, harmonics alter the “pure/ideal” output signal.

Also, you said that the latency between visual output and audio output on the Kasina was about 10 milliseconds. That would make sense if either 48000 Hz or 44100 Hz was divided by 128. That’s roughly 10 ms, and so it might give us a clue to the filters’ size.

Finally, another thing I have found that can compromise the visual signal output with glitches when pushed to faster entrainment frequencies is the headroom and EQ’ing of the overall mix of the session. You can test this by disabling all other audio except the visual output and seeing if you still have the frame dropouts and issues. If the visual signal improves with all other audio muted (including isochronic/binaural and vibration tones), it means you will need to play with the levels of your mix to find a happy balance. The output signal of AS/SS tones can be adjusted in the Settings screen of Prism, as well as an easy way to disable/enable the output of various elements. But be careful not to push the AS/SS tones too high in dB as this can lead to audible noise and other issues.

I know this post was a bit technical, so let me know if it was valuable, or clear as mud.

About as clear as when Robert tried to explain it to me :smirk:

I hear you on low pass filters on soundtracks. Rain especially effects AS and SS signals.

What would you think the optimum waveform combination would be for a 40 Hz flicker? The best I can get is a barely perceivable flicker that kind of wavers and flickers at odd times.

Some waveforms will make the light track audible with clicks and such. Is there a waveform smoother adjustment?