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Subject: Re: USB Design. Need advice.
Date: Fri, 27 Dec 2002 04:01:49 -0000
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
> Hi. I need to make an isochronus usb device that has two audio out
> and two in.
> I'm new to USB but have a decent background in electronics.
> My question is pretty simple. I can rig up a USB-DAC IC to get a singe
> audio out channel. Now if i use two of these ICs and put them behind a
> USB-Hub IC then with appropriate drivers I can send the digital streams to
> each IC, which are essentially separate devices. Similarly, I can rig up
> two ADC-USB circuits and put them behind this same internal hub. Bang it
> all in a box, stick some phono plugs on and a usb cable and with any luck
> can get down to writing the software.
> This all seems pretty sloppy though and there must be a way I can combine
> all this stuff into one device without this whole hub idea. Trouble is,
> never used USB before and should really do some reading. Theres so much
> the net though its hard to wade through all the irrelevant stuff.
> Im planning to build my own version of www.finalscratch.com. The idea
> two vinyl turntables are plugged into the 2x IN channels, the two out
> channels get connected to the DJ mixer console. The two vinyl disks that
> are put onto each turntable respectively, are pressed with some sort of
> waveform that can be interpreted digitally as a timeline. (waiting on a
> replacement LP from Stantons FinalScratch - in post so I can see how it
> works and rip it off - cheaper than having my own vinyl pressed several
> times until I got the right idea!). The idea is that two mp3s are
> out the interface into the mixer. The timebase of each mp3 is mapped to
> controlled by the vinyl. Thus you can manipulate mp3s exactly like vinyl.
> Why do I want to do this? Well apart from the $500 price tag for the
> original FinalScratch, its an interesting project.
Before you dive into USB - why not try getting a prototype running with a
You can have up to 8 inputs from 8 devices (more if you know how) Or if you
put the stereo data in, just 4 devices.
I.e, 3 Decks or 2 Decks 1 CD player, etc.
I'm pretty sure Maxim IC's had designed a few chips suitable for refining
the waveform (Square wave i'd imagine). Suitable to put into PPort
I wonder if the LP's work in stereo - pulses differential i'd imagine, so u
may need a decoder on each channel and a gate to simplify (helping u code
Maybe something to see what the volume from the mixer is to change volume on
Then the rest is software based. Option of either time-stretch (sample
looping, giving impression its playing slow, but at same pitch) or pitch.
If you do decide on the parallel port approach - i'd be interested to see if
i could build in your footsteps, seeing if i get results and see what could
be improved, etc.
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