speakers

[Bradford Miller]

So I just noticed, in this picture: https://www.columbia.edu/cu/computinghistory/pdp1a.jpg the speakers seem to be surrounded by some knobs or switches. Anyone know what they were for?

[Bill E]

No idea, but it did spark a question - just how does the speaker setup in the PiDP-1 work? It's clearly via the USB port, but how does it get there? The real -1 used 4 bits of program flags to drive 4 RC filters that were then summed and sent to an amplifier. So, 4 part polyphony was possible. The tones were generated by toggling the program flags at the proper rates to produce notes. Has this been emulated, or is there some other mechanism?

Bill

[Angelo Papenhoff/aap]

Currently the pdp1 emulator is using SDL audio so it uses whatever hardware is available to SDL. the code is extremely simple, but i am not very knowledgeable about audio so maybe someone who knows their stuff might be interested in adding some filters or knob-settings to the code to make it more real. One thing that would be nice to have is to play audio over the web interface but implementing that sounds a bit difficult....maybe in the future

[Oscar Vermeulen]

Brad,

On Saturday, September 6, 2025 at 7:16:31 PM UTC+2 bradford...@gmail.com wrote:

So I just noticed, in this picture: https://www.columbia.edu/cu/computinghistory/pdp1a.jpg the speakers seem to be surrounded by some knobs or switches. Anyone know what they were for?

I would love to know as well! As you can see, I left the mount holes for these knobs or switches on the replica speaker panel. Theoretically, we could use them as extra buttons feeding into the simulator. But their purpose is unclear. And not all of the mount holes in the real Livermore PDP-1 have been used for buttons either.

Kind regards,

Oscar.

 

[Norbert Landsteiner]

The LLNL production prototype at LLNL (they had several PDP-1s) was heavily modified.

Notice the telephone handset? This was actually for speech input!

Sound output was quadrophonic with 10-bit digital-to-analog converters (DACs).

There are 6 knobs in total (as can be seen in the attached image). I have no idea what they were for (but we may assume that there were individual gain/volume controls, which would account for 4 of them, and may be some master controls?)

More info can be found here: https://www.computer-history.info/Page4.dir/pages/PDP.1.dir/

And here: https://www.computer-history.info/Page1.dir/pages/DeSaussure.html

(The various PDP-1s at LLNL had a RAND tablet and a mouse attached, probably well before the Mother of all Demos, also optical input/scanning devices, e.g., "eye-ball". The production prototype installation also featured 4 IBM tape drives, which made it probably the largest and best equipped PDP-1 installation.)