Audacity Auto-Corrects Sound Input

[Sound_Student]

Hi everyone.

I downloaded Audacity off of a recommendation to use as a recording and analysis platform for a project I am doing. To get familiar with the process, I was recording the sound of car engines at various RPMs. While doing this, I noticed that for the first second, the sound levels would be much higher then would drop off. This difference could be noticed during playback. It seemed that Audacity was correcting at least the volume of the sound; for the project, I am trying to analyze the sound itself, and can not have any corrections.


This is the window for the 3500 RPM test. The sound seems to change as recording goes on, going from a large pattern to a much smaller one. I would think this would be the car itself, but the same pattern was observed again:


when the car was measured at 2500 RPM. I was wondering if anyone knew how to turn off this process so as to record the sound unaltered.

Thank you,
Sound_Student

[kozikowski]

Audacity isn't doing that. That's a Windows problem. Windows comes out of the box as a corporate internet communications device (Skype, Vidyo, Windows Meeting), etc., Not an entertainment recorder. You are experiencing Echo Cancellation or Auto Level Control.

-- Windows Conferencing Services
http://forum.audacityteam.org/viewtopic ... 79&start=0
http://manual.audacityteam.org/man/FAQ: ... hancements

Skype has their own, so you might not want those services anyway.

Koz

[Sound_Student]

Thank you. I applied the fixes and while it has worked, the sound volume levels are much lower than they were before. Any ideas?

[Sound_Student]

Ok, I disabled all the sound effects and recorded the engines. However, when I used the "Plot Spectrum" tool to plot the frequencies, everything came out the same. Any sound I took had the same frequency, just with different decibel levels. Is this to be expected or is there something wrong that is changing the recording? When I turned on the Acoustic Echo Cancellation and recorded again, the spectrum analysis came up with many more frequencies. Why is this happening?