The aim of this listening test is to compare the smoothness of two different morphing algorithms applied to musical instrument sounds.

Sound Morphing

The principle of sound morphing is to gradually transform a source sound to become more and more similar to a target sound. One important factor when judging the quality of a sound morphing algorithm is the smoothness of the transformation.

The Test

In this listening test you will be asked to compare the smoothness of two different morphing algorithms. Below, you will find a table with 11 pairs of morphing transformations. Each pair is a morph between the same source and target sounds using one of the algorithms. The transformation on the lefthand side is always labeled Morph A, and the transformation on the righthand side is always labeled Morph B. However, sometimes Morph A corresponds to one algorithm, sometimes to the other, in order not to bias the results.


For each morphing algorithm, you will hear eleven sounds. The source sound labeled 0.0, nine intermediate versions labeled 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and the target sound labeled 1.0. The intermediate versions are a morphing transformation from the source sound labeled 0.0 to the target sound labeled 1.0, and they should start similar to the first sound and become more and more similar to the second sound as the labels increase from 0.1 to 0.9.


A smooth morphing algorithm should produce intermediate versions that become gradually or smoothly similar to the target sound. In other words, the intervals between succesive sounds should be the same, without bumps or sudden discontinuities.

As an example of a bumpy morph, listen to the following transformation paying careful attention to the difference between the intervals. In this example, all the intervals sound very different from one another.

Bumpy Morph

Now listen to an example of a smoother morph between the same sounds.

Smoother Morph

Your Task

Your task is to listen to both morphs on each row of the table below and compare their smoothnes. Click on the button corresponding to the morph that you judge to be the smoother between the two, Morph A or Morph B. If they both sound as smooth to you then click on the no preference button. 

Remember that sometimes Morph A corresponds to one morphing algorithm being compared, sometimes to the other in order not to bias the results. In other words, if you always prefer Morph A this does NOT mean that you always prefer one morphing algorithm.

Notice that you should try to judge only the smoothness of the morph, not the synthesis quality (possible synthesis artifacts must NOT affect your judgement).


  • Check that the Flash plugin works correctly and the sound level is properly set;
  • Use headphones or earphones;
  • Do the test in a quiet place;
  • Before running the test, do not hesitate to send me an e-mail if you have questions.

Thank you for participating! This experiment won't take you more than 10 minutes.

Morph # Prefer A Morph A No Preference Morph B Prefer B

Some information about you

Listening conditions headphones other

Expertise (are you familiar with a domain related to music, such as acoustic signal processing, music technology, ... ?) yes no


Mail address and name



Before sending please check that all the files of the main experiment got an answer.

Click on "submit" to send your result!!