[ErickC]

This came about in a PM, so I thought I would post the procedure I use for general knowledge.

Quote

First, you need to do a different SMS file for every wheel size because the timing of the flat spot noises depends on the circumference of the wheels.

So the process I use is like this:

1.) Create the clips. Count the number of flat spot hits in the clip and divide by the clip length. This gives the number of revolutions per second. Multiply by 60 to get the revolutions per minute.

2.) Figure out what speed you want to be the maximum. Use this website to calculate the RPM for that speed for the wheel size you are using. Common US sizes are 33 and 36 inches. I did SMS files for 28 inches, 33 inches, 36 inches, and 38 inches, and had to calculate the RPM for a given top speed for each one.

3.) Take that calculated RPM and divide it by the calculated RPM of your clip from step 1. Multiply by the sample rate of the audio sample. This is the frequency value for the top speed. Make sure your speed is converted to m/s for the frequency curve, because that's what OR uses.

4.) You can't divide by zero, so for the minimum speed in the frequency curve, I use 1 m/s. Divide 1 by the maximum speed you set and multiply by the frequency you calculated in step 3. This is the frequency at 1 m/s.

5.) The car needs to be able to move forward and backwards, so the resulting frequency curve in this sample needs to have both positive and negative values.

You'd also need to build a volume curve where the volume is relatively high at 29.0576 m/s and zero at 1 m/s.

[ErickC]

Example: let's say I have a flat spot clip 5.4 seconds long, and you hear the flat spot hit 7 times. PLOK-PLOK-PLOK-PLOK-PLOK-PLOK-PLOK. Let's say the SMS I am building is for a car with 36 inch wheels.

1.) Divide the number of hits by the clip length. 7 revolutions/5.4 seconds = 1.296 RPS

2.) Multiply by 60. 77.778 RPM.

3.) Go to this website. Select "manual entry" for both tire and rim diameter. Enter 36 inches for the rim diameter and 0 inches for the tire diameter. Let's assume we want the top speed in our curve to be 65 mph. Enter 65 mph and calculate the RPM at 65 MPH. This works out to 606.911 RPM for 36-inch wheels.

4.) Divide this by the clip RPM and multiply by the sample rate. Let's assume a 44.1Khz clip. (606.911/77.778)*44100 = 344117.6. This is the frequency value for the top speed.

5.) Divide 1 by 65 and multiply by the top speed frequency. (1/65)*344117.6 = 5294.1. This is the frequency at 1 m/s.

6.) The resulting curve should look like this:

				FrequencyCurve(
					SpeedControlled
					CurvePoints ( 4
						-29.0576		344117.6
						 -1.0000		  5294.1
						  1.0000		  5294.1
						 29.0576		344117.6
						)
					Granularity ( .001 )
				)