If you download in mp3 format on a computer, windows media player has a speed setting. I sometimes use it. Going faster than 1.4 times becomes difficult to absorb. Also, some mp3’s don’t do so well when sped up.
Btw, the time it takes when sped up is the original time divided by the speed. For example, 60 minutes at 1.4 takes about 43 minutes. Another way to look at it is t0 take the reciprocal of the speed. For example 1.33 times faster will be 75 percent. A 48 minute shiur will take 36 minutes.