Can a DSP shift lower freqencies higher? - AVS Forum
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post #1 of 11 Old 10-03-2012, 07:18 PM - Thread Starter
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Hopefully this makes sense.

Is it possible for a DSP to shift all frequencies between say 5-15 hertz up to 16hz, while not going above a certain level? or at least with that general idea?

I tried to look around for anything like this mentioned but can't seem to find much.

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post #2 of 11 Old 10-03-2012, 08:08 PM
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A custom DSP solution could probably do something like this... but I would doubt there is anything commercially available that can do that. It probably wouldn't sound very good.
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post #3 of 11 Old 10-03-2012, 08:14 PM
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Hi Shinyav,
Quote:
Originally Posted by Shinyav View Post

Is it possible for a DSP to shift all frequencies between say 5-15 hertz up to 16hz, while not going above a certain level?
I don't yet understand the question, but the answer would be 'yes'. You can do most anything within the DSP, but most of what you can do might not make any sense.

Do you mean to take all frequencies between 5 and 15 Hz, and scale them up to say 15 to 45 hz, effectively tripling the frequency?
Or do you mean adding 11 Hz to all frequencies such that the range from 5 to 15 Hz becomes 16 to 26 Hz?
Or do you mean generating a 16 Hz tone for any frequency between 5 and 15 Hz?

All of the above can be done, but it wouldn't necessarily be music.

If you have ever used Photoshop to manipulate a picture, it is similar to what a DSP can do with audio. You can do some wonderful enhancement, or you could completely mung what you have and output trash. I've written code for both.

Keep in mind that changing a frequency by anything other than a power-of-two factor will change the note to something else. In other words, a very low "A" would be 13.75 Hz. You would need to exactly double it to 27.5 Hz to keep it an "A", moving it up one octave. The next "A" would be at 55 Hz.

So what is the effect you wish to create?
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post #4 of 11 Old 10-03-2012, 08:22 PM - Thread Starter
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Or do you mean generating a 16 Hz tone for any frequency between 5 and 15 Hz?
That one, or something similar.

Thanks for the in-depth response.
Not really looking for anything musical, just to "enhance" LFE. For example in a scene where the effects are below my subs bandpass to bump them up into something my sub can produce.

Seems like the more and more I look there wouldn't be a way to implement this without being very experienced.

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post #5 of 11 Old 10-03-2012, 08:30 PM
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Im not shure its even needed. I think most scenarios where there are output around 10hz +- there is also output up and above 16hz. So for more LFE just boost a little around 16hz (if your sub can handle it)
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post #6 of 11 Old 10-03-2012, 09:27 PM - Thread Starter
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Very true, good point.

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post #7 of 11 Old 10-03-2012, 11:55 PM
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Quote:
Originally Posted by Shinyav View Post

Not really looking for anything musical, just to "enhance" LFE. For example in a scene where the effects are below my subs bandpass to bump them up into something my sub can produce.
Assuming your sub doesn't roll-off like a brick wall at 16 Hz, you can use a low-pass filter with a roll-off at 16 Hz, coupled with a large gain to "muscle" any audio below 16 Hz. I believe you could do that now with a mini-DSP or other DSP solution.

But that might damage your drivers or sound like crap. Or both. That part is beyond me (which is why I'm here).
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post #8 of 11 Old 10-04-2012, 01:13 AM
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Probably the most likely thing you could accomplish with off the shelf commercial products (maybe?) and still not completely ruin the sound would be a circuit (dsp or otherwise) that doubles frequencies 8-16Hz and quadruples frequencies 4-8Hz, adds that to the original signal, and then filter the output below 16Hz to protect your sub if desired.

This could probably be accomplished in analog by first steeply low pass filtering copies of the original input signal below 16Hz and below 8Hz, creating strong 2nd harmonic distortion (is there a straightforward analog frequency doubling circuit?), then adding those back as per above. Maybe you can find something off the shelf which gets close? Haven't played with the minidsp enough to know whether any of the open plugins allow this much flexibility. The old epicenter car sub enhancement stuff (and I think there are new equivalents) go the opposite I think, adding subharmonics at 1/2 the frequency etc.

At least by doing this the new frequencies you create will be harmonically benign for music, and for "effects" it probably wouldn't matter anyway but at least you'd hear something when those lowest frequencies are in the original signal without having to increase the gain of your sub throughout its whole range. That's what you were after, right?

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post #9 of 11 Old 10-08-2012, 02:17 PM
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This thread is recipe for failure.

First off, you need a pre-amp and source that is flat to DC (or at least 4hz @ -3db).
Do you even have that to start with?
You may want to take some REW line-level output measurements to make sure, before you waste any of your money.
You may just find out that you are rolling off at 10hz before it even hits the DSP or amp eek.gif (and then those rolloff themselves eek.gif)
Otherwise there is nothing there to multiply, right? wink.gif

The FP14k is the flatest amp I know of (1.8hz) and an XSP-1 pre-amp and Xonar soundcard will be good down to about 3hz.
Ok that's $2500 and we haven't even started yet...

Hook that to an array of bass shakers or Rotary Subwoofers and you might just have some real world results.

That sounds expensive, because it is.

Messing with the amplitude and phase of infrasonic signals, at best, it is probably going to sound like mud soup, and at worst, create a dead subwoofer.
You probably won't miss much if you can already do 16hz. But hey, it's your money and your subwoofer, spend the money on creating a customized analog DSP infrasonic multiplier thingy and report back to us how it went tongue.gif
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post #10 of 11 Old 10-08-2012, 02:53 PM
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^^ The -3dB point on almost every SS device is due to the DC blocking cap. If you want a lower 3dB frequency, change the cap to a different value. Cost would be a few $ and some time and effort.

For the OP, yes you could accomplish what you want to do. LPF filter from 16Hz, pitch shift 3x and mix that into a 16Hz HPF filtered version of the original signal stream. Some production software like Reason could (probably) do it.

The main question is why you'd want to do it?
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post #11 of 11 Old 10-08-2012, 04:55 PM
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Quote:
Originally Posted by Shinyav View Post

Hopefully this makes sense.
Is it possible for a DSP to shift all frequencies between say 5-15 hertz up to 16hz,.
Yes, but then all of those frequencies would then be 16Hz, and that doesn't make sense.

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The Laws of Physics aren't swayed by opinion.
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