On my Apple ] [ with 48k memory I used to be able to sample audio from the cassette port and store about 30 seconds of audio that was fairly decent quality upon playback. With a 1MB RAM board installed I was able to sample the entire ~5 minutes of Led Zeppelin's Over The Hills And Far Away from their Houses of the Holy album.
Sellam On Mon, Jul 10, 2023, 6:41 AM Paul Koning via cctalk <cctalk@classiccmp.org> wrote: > > > > On Jul 9, 2023, at 9:19 PM, Douglas Taylor via cctalk < > cctalk@classiccmp.org> wrote: > > > > Wow! Actual engineers responding... > > > > It looks like I could only do the most rudimentary audio. > > > > 1. Sample Rate: You got maybe 20K samples to store in lower memory. At > 7KHz sample rate that would allow 3 seconds of audio. Voice only. > > 2. Samples: They must be 12 bits. Converting a modern audio clip > requires, band filtering, resampling and mapping to 12 bit integers. Could > be done in python, they have libraries. > > 3. Clocking output: I have a KMV11, but never programmed around it. > > 4. Amplify output: AAV11-C produces -10 to +10 volts, have to divide > this down for input to an audio amp. > > > > In the end I will have undone all the advances made in digital audio in > the last 30 to 40 years. > > I'm reminded of a project I did in college in 1974, when I made a > primitive graphics display using an X/Y oscilloscope driven by an AA-11. > Since the machine was a PDP-11/20 with 8 kW of memory, I decided to use the > RC-11 disk as the refresh memory, doing DMA directly from disk to the D/A > data CSR. > > So on the scenario here: the sample rate is clearly more than adequate. > 12 bits is not CD grade audio but not bad; for ears used to the distorions > of compressed audio files it's probably good enough. > > The PDP-11 certainly won't be able to decompress modern lossy compression > files. It should be fine with raw or nearly-raw files, which means you can > convert externally and feed the resulting files to the PDP-11. You could > convert to 16 bit raw mono with standard tools and then drop the bottom 4 > bits. Band filtering? Resampling? I don't know why you would want to do > that, unless there isn't a reasonable way to drive the device at the source > file's data rate. For example, if you have a KW-11/P that's clearly > doable. (Come to think of it, that 11/20 had a KW-11/P and I created BASIC > extensions for it that would allow sampling to be driven by that clock, at > a rate of your choosing.) > > You can't fit a whole lot of data in 64 kW of memory, but that isn't > needed. That rate isn't all that high; it isn't hard to write a program > that does double buffering from a disk file to memory to the D/A. That > makes a really nice real time programming exercise. > > paul > >
