Audio Output on the USB PropDongle
LoopyByteloose
Posts: 12,537
I just noticed Terry Hitt has made a Prop platform that has USB interface with a power from the USB and about the size of a BS1 board.· It really is a beauty. I'm considering using it a bench tool for exploring the creation of sound effects on the Propeller.· These may eventually go into Hydra games or into developing speech phonemes.
It is only providing 12 bits of I/O, but I've yet to use all of the 32 I/O pins and some are usefully set aside to pass data from one Cog to another.
There is also an· RCA plug video interface included.·
To begin with, I wonder, 'Is that supported with a Sigma-Delta or R2R DAC format?"
·And, here is the· main question.·'Has anyone considered adapting the RCA video interface to synthesize a purely audio output?'
I suppose I could just as easily create·an 8 bit·R2R·network·that is explicitly for audio, but I'm not sure it would be any better.··From Guenther's SX tutorial book, I see that an 8 bit R2R network with op am is quite good.·But am I really being silly and should just directly commit to an 8 bit DAC chip?
The only other thing involving i/o pin count that I might include is an Electret microphone to do speech sampling for the phoneme creation and recording some oddball special effects.
There does appear to also·be room to have a small audio amp to drive ear phones.
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"Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
Post Edited (Kramer) : 10/6/2007 12:44:34 PM GMT
It is only providing 12 bits of I/O, but I've yet to use all of the 32 I/O pins and some are usefully set aside to pass data from one Cog to another.
There is also an· RCA plug video interface included.·
To begin with, I wonder, 'Is that supported with a Sigma-Delta or R2R DAC format?"
·And, here is the· main question.·'Has anyone considered adapting the RCA video interface to synthesize a purely audio output?'
I suppose I could just as easily create·an 8 bit·R2R·network·that is explicitly for audio, but I'm not sure it would be any better.··From Guenther's SX tutorial book, I see that an 8 bit R2R network with op am is quite good.·But am I really being silly and should just directly commit to an 8 bit DAC chip?
The only other thing involving i/o pin count that I might include is an Electret microphone to do speech sampling for the phoneme creation and recording some oddball special effects.
There does appear to also·be room to have a small audio amp to drive ear phones.
·
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"Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 10/6/2007 12:44:34 PM GMT
Comments
It sounds pretty good if done right. [noparse]:)[/noparse]
You can get 12 or 16 bits out of it without much problems. Less parts are needed as well.
As for doing this from the Video-out DAC. Then maybe you could map the 1bit audio output pin to the MSB of the 3-bit Video-DAC and leave the other 2 pins low or high depending on where you wanna bias things. Another trick would be to change all 3 pins together with the same 1-bit signal. [noparse]:)[/noparse]
--Andrew Arsenault.
- You can also generate a fine 3-bit signal in TV mode (0..7), chroma bit off. As a (current) DAC is already on most boards, just ground with a 75 Ohms resistor and buffer the signal (1V) with a low cost aop-amp or even a "real" audio amplifier
- PWM loading a cap ("one bit DAC") however is the easiest way for audio freqiencies.
If you look at the Propeller Demo Board schematic you will see that it uses a simple 10K resistor and a 10nF cap on a single pin.
http://www.parallax.com/dl/docs/prod/prop/PropDemoDschem.pdf
Let me know if you come up with something cool.
Bean.
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