16bit intensity profile for LED fade?

jcclowjcclow Registered User
Hello all...this may seem silly (which is why I'm asking) but is it possible to have an intensity channel with 16bit resolution? The reason I'm asking...I have two Luxeon K2 Star LEDs running off a Theatre Wireless RC4 Wireless DMX/dimmer and a 6v battery. When I manually roll the intensity up and down with the encoder, the fade is seamless with no "steps" in between the levels. When it runs on a sub with a 1 sec fade time, you can see steps in the fade. The RC4 specs claim smooth LED fades using an ISL curve with a resolution of 16,384 steps or 0.0061% intensity for each step (which should be an intensity change that's imperceptible to the human eye). Do you see where I'm going with this? Thanks for any input...


  • AndrisAndris Registered User
    edited August 2009
    The RC4 only has one DMX channel assigned to each dimmer, so you are stuck with 8bits on the control side. The hog can do 16bit intensity, but you need two DMX channels per dimmer to get that resolution.
    The RC4 probably interpolates the timing between DMX value steps and tries it's best to give you a smooth curve, but since you are using LEDs, the steppiness will be much more visible.
    I have yet to see a standalone LED dimmer that can do smooth dimming, especially on the low end.
  • edited August 2009
    Yes, the Hog supports 16 bit intensities. But to get the full 16 bits, you need to have a dimmer that supports 16 bit inputs, and patch it properly. The stock Desk-Channel fixture in the library is 8 bit only.

    Even though the RC4 Dimmer supports 14 bit dimming, it appears to only use a single 8 bit DMX slot. That means there is some kind of internal map between the 256 DMX levels, and the 16,384 output levels. Each of the three curves will have a different mapping.

    To understand where the steppiness is comming from, you'll need to have a good understanding of every component in your system. The fundimental problem is that the human eye can differentiate more than 256 different intensities. An 8-bit input simply isn't enough to get truely smooth fades at the low end, and full output at the other end.

    Further, the dimmer may implement some kind of filtering. Filtering is commonly used to smooth out fades over time. The downside is that filtering can delay your response time to quick bumps, so some devices try to be clever and guess what the user intended.

    Finally, there's the issue of the DMX refresh rate. The hog has a 30 Hz refresh rate by default. If the dimmer doesn't have filtering, many people can see 30 Hz updates, especially on a very fast, or very slow fade. If the wireless interface is dropping every other packet (which some wireless DMX devices do), then you have 15 Hz refresh, and 15hz will definately seem choppy without aggressive filtering.

    Controlling LEDs is hard to do right, there's much more to it than first meets the eye. I've never used the Theatre Wireless gear, but it's probably worth a phone call to them to understand how they do their control and filtering.
  • jcclowjcclow Registered User
    edited August 2009
    Thanks to both of you for the great reply. This is really me just being anal as management thinks the new design looks amazing just for the simple fact that it actually dims.
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