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# Alter running speed for sound quality jury evaluation?

Experimenter

Doing a sound quality jury test, and have two starter motor noises to be part of the evaluation.

Only problem is that these two starter motors run at different rpms.  Don’t want the jury to key in on the different speeds, but rather evaluate the sound quality difference.

Is there any way to make the two motors run at the same speed by synthetically altering the sound?

I have attached the sound files including the rpm.  Would like the 360 rpm starter to run at 468 rpm if possible

# Re: Alter running speed for sound quality jury evaluation?

Siemens Phenom

Well that is a tricky one!  But think we found an answer.

The trick is to use some of the angle domain processing capabilities of Simcenter Testlab.  Under “Tools -> Add-ins” turn on “Angle Domain Processing” and “Time Signal Calculator” (Note this also pulls a Signature Throughput Processing license).

Then use the following formulas on the 360 rpm starter motor in Time Signal Calculator:

Here is what they do, step by step:

Step 1

The first formula “CH2*(474/360)” scales the 360 rpm trace (in CH2) to 474, picture below.

This scaled rpm will be used to resample the starter sound to a higher rate.

Step 2

Then perform an integration operation with INTEGRATE(CH2/CH4;1). This creates a special time trace of time versus time:

The current recording time duration of the original 360 rpm starter motor is on the X axis (8.5 seconds).  If the starter motor speed was increased in speed to 474 rpm, the recording time duration would be decreased.  This is the value of the time on the Y-axis (5.81 seconds).

Step 3

The recording needs to be sped up by a factor of 8.5/5.81.  The next command, SYNC_RESAMPLING_CORRECTED_TIME will do this.

This command was originally developed to correct for Doppler shifts due to moving sound sources. The “function1” is the starter motor sound to be sped up.  The function2 is time versus time trace from Step 2.

Results

The new sound 474 rpm synthetic sound trace, which has been sped up, has the same amplitude as before.  The starter events occur faster.  They occur at the same rate as the 474 rpm starter motor.

The modified files are attached.  Hope that helps!