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FFB Types

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nlp80 edited this page May 12, 2017 · 5 revisions

FFB Types

Note: This page refers to modes that were available in older versions of irFFB. Most have been removed from recent versions.

The FFB types are divided into 2 main categories; those that are based on the iRacing telemetry output and those that are based on the normal, DirectInput FFB output ('direct' modes). iRacing updates the telemetry near the end of each iteration of it's main loop (which is run 60 times per second) and the modes that are based on telemetry therefore have a minimum latency of ~ 15 ms. The minimum latency of the direct modes is the same as the normal iRacing FFB. Where approximate latencies are listed, they are referenced to the normal iRacing FFB.

  • 60 Hz - SteeringWheelTorque telemetry data written out immediately to your wheel. Input rate: 60 Hz / Output rate: 60 Hz. Total extra latency ~ telemetry latency (15 ms).

  • 120 Hz - SteeringWheelTorque_ST telemetry data fed at 120 Hz - we only use 2 samples of the available 6 and throw the rest away. Input rate: 6 x 60 Hz / Output rate: 120 Hz. Total extra latency ~ telemetry latency + 8 ms (23 ms).

  • 360 Hz - SteeringWheelTorque_ST telemetry data written out with a necessary delay to space the samples out in time. Input rate: 6 x 60 Hz / Output rate: 360 Hz. Total extra latency ~ telemetry latency + 14 ms (29 ms).

  • 60 Hz interpolated - the 60 Hz SteeringWheelTorque data with an extra 14ms delay that we fill in with a cosine interpolation between the last sample and the current one. Input rate: 60 Hz / Output rate: 360 Hz. Total extra latency ~ telemetry latency + 14 ms (29 ms).

  • 360 Hz interpolated - SteeringWheelTorque_ST telemetry data with linear interpolation between samples to give 720 Hz output. Input rate: 6 x 60 Hz / Output rate: 720 Hz. Total extra latency ~ Fixed latency + 14 ms (29 ms)

  • 60 Hz direct - iRacing FFB direct. Input rate: 60 Hz / Output rate: 60 Hz. Controlled by iRacing settings. Total extra latency ~ 0 (0 ms)

  • 60 Hz direct interpolated - iRacing FFB direct with cosine interpolation. Controlled by iRacing settings. Input rate: 60 Hz / Output rate: 360 Hz. Total extra latency ~ 14 ms (14 ms)

  • 60 Hz direct filtered - iRacing FFB direct, upsampled and passed through a low-latency digital FIR filter. Controlled by iRacing settings (in irFFB < 1.3). Input rate: 60 Hz / Output rate: 360 Hz. Total extra latency ~ a few ms (a few ms)

The following graph depicts a number of the different types with each offset in the Y axis for visibility. The offsets in the X (time) axis are an indication of the relative latencies. In terms of shape the bottom-most trace (360 Hz) should be considered the reference as it is the best indication available of what the physics output should look like. In terms of latency, the top-most trace (60 Hz direct) should be considered the reference since it is equivalent to the standard iRacing FFB.

From top to bottom, the traces are:

  1. (blue) 60 Hz direct
  2. (black) 60 Hz direct filtered
  3. (green) 60 Hz interpolated (linear interpolation)
  4. (red) 60 Hz interpolated (cosine interpolation)
  5. (yellow) 120 Hz
  6. (magenta) 360 Hz

ffb graph

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