Bit / Sample Rate Reducer

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Topic: Bit / Sample Rate Reducer

JAnthony
Member

posted 02 March 2003 21:46 Edit/Delete Message

Hello,

I was wondering if someone could tell me how to construct a bit rate reducer and a sample rate reducer?

Thanks

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pete
Member

posted 03 March 2003 08:34 Edit/Delete Message

Hi JAnthony

The bit resolution reducer can be done by using two gain modules one after the other. If the first module
has 1/2 as its gain and the second has 2 as its gain, then the level at the output will be the same but with the
last bit removed (23 bits). If you do the same but with 1/4 and 4 in the two modules gain fields, you will get 22 bits resolution. If you need help with a formula to make it hot adjustable all the way down to 1 bit, let me know.

When a sample rate is reduced, it is normal to lower the frequency of the output filter on the D to A convertor to get rid of the HF Buzz. Putting the signal through a low pass filter would give you the same result.
But I suspect that you want to hear the HF Buzz. If this is the case let me know and I'll try to think of a way of doing it.

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SSC
Administrator

posted 03 March 2003 09:43 Edit/Delete Message

If you want a sample rate reduction "effect", you can use the SampleAndHold module. Set the HoldTime to

!DesiredSampleRate hz inverse

and in the VCS change the range of !DesiredSampleRate from its initial 0 to 1 range to a more suitable range (like 100 to 10000).

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keph
Member

posted 03 March 2003 12:28 Edit/Delete Message

quote:
Originally posted by pete:
Hi JAnthony

last bit removed (23 bits). If you do the same but with 1/4 and 4 in the two modules gain fields, you will get 22 bits resolution. If you need help with a formula to make it hot adjustable all the way down to 1 bit, let me know.

does it progress at 1/n*2 or 1/n^2? currently, i use equal gain to attenuation which is a cheat and doesn't let me know the bit rate, i dial it in by ear. stops working around -137.5db if i remember right (been a few years since i looked at that sound.)

the correct formula would allow a better mimic in delays and filters around lower bit rates (for some reason i got really into this and down sampling a few years ago:)

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JAnthony
Member

posted 03 March 2003 19:51 Edit/Delete Message

BitReducer.kym

Thanks for your help everyone...

Pete, I've attached my attempt at the Bit Reducer, I think it is done correctly but I'm not sure if the formula I used was the best way to go about it.... what do you think?

Also, it makes no sound at 1 Bit. I expected this ay 0 Bit , but shouldn't 1 Bit produce sound?

Thanks again

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pete
Member

posted 04 March 2003 07:40 Edit/Delete Message

BitRed2.kym

Hi JAnthony and keph

The formula is (24-bits)^2 and its inverse of cause.

JAnthony ,I think your formula amounts to the same thing and your right , one bit should make sound. If you turn off
the grid in your example, you will find that one bit sound is produced if you move the hot parameter up the most tiniest
little bit over one. This is because math's on computers are never 100% perfect. So in my attached version I've
introduced a tiny error (23.9999 instead of 24) to compensate. This shouldn't make any difference to the normal operation.

hope it helps.

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JAnthony
Member

posted 04 March 2003 13:49 Edit/Delete Message

Pete,

That's a great idea... I should of thought of it.

Thanks for checking my work!

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