Purposely messing with a deck's bias frequency

[lo.fi.love]

I'm currently reading the book about the San Francisco Tape Music Center. It has a fantastic collection of interviews with the center's founders and participants. It is a GREAT book and I recommend that everyone here check it out and consider buying it!

I'm curious to know about one technique that is briefly described in the book, where a signal is generated using an oscillator and fed into a tape deck. It is either at or near the deck's bias frequency and sending this tone to the deck causes it to distort and/or otherwise malfunction in interesting and artistically 'useful' ways. I believe that Pauline Oliveros mentioned discovering this effect for herself while working on her composition "Bye Bye Butterfly".

Does anyone know what this means, what this phenomenon is, and why it occurs? I'm very curious to know.

The question is, how does one execute this? A quick Google search reveals that the TASCAM 32's bias frequency is 150kHz, and the 122 mkii cassette deck has its bias frequency at 100kHz. This seems really high, and I definitely won't be able to achieve this frequency with any kind of software-based oscillator (like the one in Audacity, for example).

Maybe someone with a more hands-on understanding of magnetic recording might have an idea what this is and how it's done. Anyone?

Thanks!! I'm very eager to see if anyone has something to say about this.

[dintymoore]

I've never heard of it but it sounds like it creates some synth functions.

Around 1975 I was in a band that bought a Yamaha p.a. mixer and the keyboard player found that by plugging an output into an input the thing would oscillate in very strange, musical ways and that he could even play it with the knobs. I used to jam along with it on drums, and it wasn't just one stupid sound, he could manipulate it and we'd jam for a long time. Some of the oscillations it got going were a riot - real funny burps and farts and quacks but in a looping rhythm.

We called it "The Great Yamaha" like it was a spirit coming through the mixer.

[lo.fi.love]

Hmm. It may be worth it to buy an oscillator, actually. Here's a handheld one that I've found on the web, and it generates square & sine waves from 20Hz to 150kHz: Link

Could be useful for a number of applications, not just creating weird sounds. Use it to key a gate, calibrate tape decks, etc.