Throughout most of the original STAR TREK series, the sound effects used for buttons, switches and other controls aboard Federation spacecraft sounded essentially the same. There seemed to be an established kind of musical vocabulary to the sounds made when many controls were used whether it was stations of the Bridge, Engineering, or the Transporter Room of the Enterprise or even some controls aboard a shuttlecraft. Then, partway through the show's third year, this set of sound effects changed considerably. It was no longer as musical as before, and it sounded much more like touch-tones than the previous set did. There was another change: buttons without the melodic sound effects, which typically had a "snap" sound effect applied to them, were given a newer sound effect I can a "button" effect, right from the beginning of the show's third year. Why did all of these sound effects change? What was the first episode of TOS Year 3 to use the "new" touch-tone-like sound effects? Where did all of these control panel sound effects originate from? Why didn't the TOS producers simply stick to the first set of sound effects for consistency? It is interesting that TOS-oriented fan films such as "The Tressaurian Intersection" and "Fairest of Them All" mix the two sets of sound effects together.