Linearly increase/reduce intensity

I’m using Audacity 2.4.2 on Windows 10

Hi,

I need to generate some audio stimuli for a psychology experiment and I am really struggling to figure it out myself (I have no prior experience in sound engineering/acoustics or any kind of audio editing…)

Essentially what I am trying to do is create a series of sounds starting from a 5-second 440Hz tone where the intensity/volume of the sound increases or decreases linearly. I am looking to end up with 3 sounds (each 5s long):

  1. the tone linearly increases from quiet to loud
  2. the tone linearly decreases from loud to quiet (i.e. the opposite of 1)
  3. a stereo track in which the 1 channel increases (panned left) and the other decreases (panned right) so that you get a left-right type effect when wearing headphones

The goal is then to play the sounds so that there is an exponential change in sound pressure level from 70dB to 55dB (and vice versa) during a sensory perception task.

I have had a go by looking through the documentation and using the envelope tool but I have no idea if I am on the right track at all and this method doesn’t seem like it would be possible to make the increase/decrease actually linear? I have attached a copy of the tone I have been using and my 3 attempts at the sound types.

Basically, my two questions are:

  1. Is there a way to create this type of linear change in intensity (i.e. the same rate of change) in a reliable way?
  2. Is there a way to make sure that the sounds would be within the correct spl range at the editing stage? Or is this something that would be controlled by the hardware used for the experiment (i.e. I would need to wait until I can get into the lab with a sound level meter?

Apologies if these are incredibly basic questions and/or very obvious! I am trying to figure this out from home (with no equipment) and absolutely no prior experience :neutral_face: :laughing:

Thank you!

“Generate menu > Tone” (See: Tone - Audacity Manual)


“Effect menu > Fade In”
“Effect menu > Fade Out”
(See: Fades - Audacity Manual)


Make the two channels as separate mono tracks, then join them to create a stereo track.
See here: Splitting and Joining Stereo Tracks - Audacity Manual


Not in Audacity. The SPL depends on the volume of your playback system.
You could have a really “loud” sound in Audacity, but if you turn down your headphone volume then it will be quiet (low SPL).

The regular fade-in and fade-out are linear but you’re ears and decibels are not…

There is also a Studio Fade Out. With a pure-tone you could reverse the audio to get a similar/complementary fade-in. That’s probably useless for “science”.

The [u]User Manual[/u] has a “hint” for approximating an exponential fade. This probably also isn’t good enough for science.

You can do “almost anything” with [u]Nyquist Programming[/u] but that does require programming.

  1. Is there a way to make sure that the sounds would be within the correct spl range at the editing stage? Or is this something that would be controlled by the hardware used for the experiment (i.e. I would need to wait until I can get into the lab with a sound level meter?

Right… You have to calibrate with an SPL meter. The acoustic loudness depends on many factors including amplifier power and the volume control setting, speaker sensitivity, how close you are to the speaker, and room acoustics.

There is a direct correlation between dBFS (digital) and dB SPL (acoustic) so if you decrease the digital level by 3dB the SPL also goes down by 3dB, etc. That’s assuming everything is linear… You’re not overdriving and clipping the amplifier, etc.

A little trick in Audacity to help you do the fade in/out:

If you Generate a 5 second 440Hz tone, and this corresponds to your 75dB, and if you duplicate this track (Ctrl+D), then select this second track, amplify it by some number, say -30, and this (via SOLO) corresponds to your 55dB requirement, then:

  1. Do a fade in on the first track. (This will go from 0 to 75dB).
  2. Export or play, or mix and render. (This will go from 55dB to 75dB).

I hope this helps. :smiley: