Audacity Forum

Hi there, I have been using audacity for a university project and have been very impressed with it's functionality so far. I just have one question and was wandering if anybody here knew the answer..

I have been generating test tones using audacity, and the amplitude of each test tone is user changeable, on a scale of 0 - 1. Does anybody know if this is on a linear, or other scale? For example, would a tone with amplitude 0.4 be twice as loud as a tone with amplitude 0.2 ?

I would appreciate any help / thoughts on this.

Cheers!

s

Amplitude 0.4 would (other factors being equal) be twice the voltage of 0.2 on the sound card output. It wouldn't sound twice as loud because your hearing system is broadly logarithmic in nature. I believe that to get a doubling in percieved volume you have to raise the sound pressure level by a factor of 10. How that relates to the signal level in audacity depends a bit on the hardware between one and the other, but broadly the percived volume relates to the log to base 20 of the signal level (a squared term to convert voltage to power, and a log to base 10 for decibels).

...and you can see all of that happening by converting your timeline to dB. It's the little black down arrow to the left of the timeline. Select Waveform (dB). Grab the bottom of your timeline and pull down as far as you can. The numbers up the left side of the timeline will get more and more accurate as they get taller.

I would create all my test tones at the same level and use the Effect > Amplify tool to modify them to the level you actually want. That tool will give you tenth-dB control over your work. Much, much finer control than the generator tool.

Yes, half or double audio voltage is 6dB, but your ear doesn't hear half and double until the sound hits roughly 18 dB up or down. About ten times higher or lower than the original. Your ear works a little wacky which is why 0-1 (0-100) percentages aren't very useful to measure sound. The waveforms in 1.2.x aren't marked very well, either, so it's an adventure to actually measure sound values if you don't know what they are ahead of time.

Koz

Thank you for your comments guys.

Our ears do indeed work in mysterious ways, let alone how we perceive sound!

I will be discussing my results relatively as opposed to in relation to a dB / SPL scale so no need to try to work out actual SPL at the headphone output - as you say it depends very much on the hardware in between audacity and the listener.

s