The pitch of a sound is its frequency. Growing the frequency of a sound will increase the pitch. Conversely, lowering the frequency lowers the pitch. How do you alter the frequency? Properly, in case you have a recording, you possibly can merely alter the playback velocity. Most vinyl file followers have skilled this for themselves because of by chance setting the turntable to the incorrect RPM. However what in order for you the identical impact in real-time? Sam Battle of LOOK MUM NO COMPUTER discovered a really intelligent analog answer primarily based on a tape loop.
If you happen to’re pondering that this impact is so simple as working a tape loop, just like a standard tape delay, at a variable velocity, then you definitely’re not absolutely contemplating the ramifications of the real-time side. Battle couldn’t simply run the tape loop sooner to extend pitch, as a result of the gadget must file on the identical time it performs. Apart from a really slight delay (the gap between the recording head and the playback head), the recording velocity and playback velocity would match and there wouldn’t be any shift in pitch. The issue is trivial with digital sign processing, however appears not possible to resolve utilizing an analog tape loop like this.
The ingenious answer dates again to not less than a design for a “tempophone” from the Nineteen Sixties. It really works by transferring the playback heads (sure, plural) relative to the conventional velocity of the magnetic tape. That’s potential as a result of the playback heads (4 of them on this gadget) mount on a spinning wheel. If that wheel spins backwards, relative to the tape, it’s successfully slowing down the playback velocity and subsequently dropping the pitch. If the wheel spins forwards, it’s growing the playback velocity and the pitch.
The rationale the tempophone association is so intelligent is that it solves the real-time impact downside. After all, it might probably’t truly play again audio sooner than that audio is being recorded, as a result of time is a factor. What it’s truly doing is making the most of the slight delay between some extent on the tape crossing over the recording head and the identical level reaching the spinning playback heads. The playback heads then transfer over that brief size of tape both sooner or slower than regular. It naturally makes up for the “gained” time (or misplaced time, in a pitch drop) by clipping till the subsequent head on the wheel comes round.
That clipping does produce a form of warbling sound, however that’s fairly neat in its personal proper.
Battle constructed his personal tempophone-style real-time pitch shifter utilizing 3D-printed mounts on sheet metallic, some customary tape deck components, one stepper motor to feed the tape, and one other stepper motor to spin the playback heads. Two Arduino Nano boards management these motors in keeping with enter from potentiometers.