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Klaas Robers wrote:The nice thing of a CD-player is that you don't have to bother about the sound. That is analoguely coming out of the red output. If you stored and read back the wave file, then you have to see that you play it in the proper speed and you have to handle the 16 bits sound channel.
But there is another way. The better CD-players output next to L and R analogue audio as well a digital data stream. It is a fast serial stream, but that can be parallelised by a certain IC. Together with Vic and Karen we did this for Compatible Colour NBTV. May be you could look into what Vic did and use the same circuit. Then you have direct access to the digital data stream of the left channel of the running CD. And also here, the sound channel is not processed, it is already analogue.
gary wrote:You are using 44.1kHz? That's making a rod for your own back.
gary wrote:*Not* doing that will make it a) harder to process the sync pulses (because their edges fall between the samples) and b) introduce aliasing effects into the picture.
gary wrote:My previous (perhaps hasty) assertion that you won't need a reconstruction filter was predicated on there being an integer multiple relationship between the signal and both the sample rate and the modulation frequency (which itself should be an integer multiple of the signal sample rate).
gary wrote:Having said all that, your system is showing great promise.
gary wrote:Does that mean I'll have to buy The White Album *again* ????
Klaas Robers wrote:I wonder what the PWM generator does if you change the value while it is going. This is because the pixel clock is in almost the same speed as the PWM clock, so reprogramming the PWM value is done quite frequently.
And then you have an extra problem, because when PWM modulating the LED brightness you have a linear system. Your eyes are no linear, that is where the gamma comes in. If you want to have 64 grey levels in the eye apreciation then you need 3 bits more, i.e. 512 levels of brightness.
If your clock frequency is 16 MHz, and with 512 levels, the PWM frequency will be 32 kHz. Rather low, as your pixel speed is about 20 kHz......
gary wrote:It's a tried and proven approach Andrew, are you an NBTVA member? There are examples in the Newsletters.
Klaas Robers wrote:I wonder what the PWM generator does if you change the value while it is going.
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