![]() The ‘crude’ version is a direct implementation of the algorithm as presented on the scheme above, the ‘smart’ version uses the resampling facility of SciPy and is significantly faster. The following code is a command-line tool to create the slow-motion or ‘chipmunk’ sound effect. It contains an even broader perspective on the variable speed replay algorithm and many more it is one of the best books to learn about audio algorithms! Code example If you want to learn more I highly encourage you to check out this book “Digital Audio FX” by Udo Zölzer et. We have discussed the variable speed replay algorithm, which enables to manipulate the relative feeling of time flow in the signal and explored its consequences and applications. However, they are likely to appear in the future WolfSound’s articles, so stay tuned! Summary Here, a variety of Overlap-Add methods apply, which are beyond the scope of this article. It is not trivial to scale the signal in time without altering the pitch (i.e. Thus the corresponding Time.fixedDeltaTime parameter should be updated accordingly (typically Time.fixedDeltaTime = 0.02f * Time.timeScale, where 0.02f denotes the typical default value of Time.fixedDeltaTime, but it can be different of course). Note: the Time.timeScale parameter also does not change the rate at which physics engine is updating. Read the corresponding Unity manual parts here for the timeScale parameter and here for the pitch parameter. ![]() It doesn’t change the pitch and time duration of audio though, but… you could do that using the algorithm described here! Actually that’s what the pitch parameter of AudioSource component does: it changes pitch and time simultaneously, taking advantage of the Variable Speed Replay algorithm. If set to 1 the time flows normally, however, if you decrease it to 0.5 the events happen two times slower, so the Time.timeScale parameter corresponds to the v v v parameter in the variable speed replay algorithm. It basically changes the speed at which things are happening. If you ever worked with the Unity Editor, you may have stumbled upon the Time.timeScale parameter. Keeping the v v v ‘s value negative we can change the scaling of the inversed time signal… What gives an enormous amount of possibilities! Check out this example in Ludger Brümmer’s “The Gates Of H” musique concreté piece.Ībove examples show that variable speed replay algorithm is a creative application of the sampling theory. solo on “ Misunderstood” by Dream Theater has been time-reversed (check out the whole story on Wikipedia) or ending of “ A Day in the Life” by The Beatles, where one can hear reversed recordings being played in a loop. If we set v = − 1 v=-1 v = − 1 we get… a time-reversed signal! This technique is extremely powerful, especially in experimental or progressive music, e.g. the vibrato technique (changing the frequency of the instrument in a certain range around the played note) loses its characteristics: it becomes a slower (when slowing down time) or faster modulation.the transients are spread (slower) or contracted (more rapid),.The time structure is altered with the following perceivable changes: if we are slowing the signal (scaling the time speed down) we perceive a “slow motion” effect (exactly like the one in “Inception” or “The Matrix”).if we are quickening the signal (scaling the time speed up) we receive a “Mickey Mouse” or a “Chipmunk” effect (especially powerful when applied to speech),.The frequency structure changes with the scaling accordingly: We can reason about the result of such signal rescaling in two domains: time and frequency. The outcome of variable speed replay application We can see, that the duration of the sine shrunk to 2.5 ms, what is no surprise, since we basically removed half of the signal and 2.5 ms corresponds to half of 5 ms.īut if duration changed, with sample rate remaining constant, the frequency changed as well! The new period length is 1 ms, so the frequency of the sine is not 500 Hz anymore, but 1 0.001 = 1000 \frac f s, in and thus the difference in pitch when playing it out. The signal after removing every other sample. Let’s note, that one period is 2 ms long. Here we have a 500 Hz sine wave sampled at 16 kHz: What would happen if we removed every other sample from the signal? To simplify things, let’s look at an example. If you need a revision on aliasing check out this article. If you don’t know what sampling is all about check out this article. ![]() In this article we will prove the usefulness of the sampling theory in music and audio effects. ![]() Do you remember the slowdown of time in “Inception”? Or the “bullet time” in “The Matrix”? How to create such a slow motion effect in the audio domain? That is the topic of today’s article! ![]()
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