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On 04-Nov-08 20:14, Orchid XP v8 wrote:
> I should probably go read a book or something...
Why?
Remember Westheimer's Discovery: A couple of months in the laboratory
can frequently save a couple of hours in the library
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Would help if I actually wrote something before posting... ;-)
> I want to split a sound signal
Don't worry about the phase of the signals then, your ears don't care. In
hardware filters the phase is rarely preserved, and actually often varies as
a function of frequency. Just make sure the phase shift is the same for the
Left and Right channels, otherwise you might mess up some stereo effect.
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> (Btw, did you know that even if a sound signal has only one single
> frequency, a discrete fourier transform is usually completely unable
> to find that single frequency, and instead will find a large (potentially
> infinite) amount of frequencies around that real frequency?)
It just depends how many samples you use for your fourier transform, the
more samples you take, the more accurately you can divide up the frequency
spectrum. If you have a couple of seconds of normal audio recording (so
like 100k samples), you should be able to find a single frequency pretty
accurately, certainly to within 1 Hz.
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scott wrote:
> Would help if I actually wrote something before posting... ;-)
>
>> I want to split a sound signal
>
> Don't worry about the phase of the signals then, your ears don't care.
> In hardware filters the phase is rarely preserved, and actually often
> varies as a function of frequency. Just make sure the phase shift is
> the same for the Left and Right channels, otherwise you might mess up
> some stereo effect.
More significantly, if the same frequency is present in more than one
channel, phase will matter. (I still need to add the channels back
together again and end up with the same signal as before, which won't
happen if phase differences cause spurious boosting/cutting.)
Besides, in a digital FIR filter, it's trivial to make the filter
zero-phase.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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scott <sco### [at] scott com> wrote:
> > (Btw, did you know that even if a sound signal has only one single
> > frequency, a discrete fourier transform is usually completely unable
> > to find that single frequency, and instead will find a large (potentially
> > infinite) amount of frequencies around that real frequency?)
> It just depends how many samples you use for your fourier transform, the
> more samples you take, the more accurately you can divide up the frequency
> spectrum. If you have a couple of seconds of normal audio recording (so
> like 100k samples), you should be able to find a single frequency pretty
> accurately, certainly to within 1 Hz.
If the actual frequency falls in between two frequencies of the DFT,
there's no way for the DFT to produce just one or a few lines. Only if
the frequency happens to be exactly on one of the frequencies sampled
by the DFT, it will generate one single line.
--
- Warp
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Orchid XP v8 wrote:
> More significantly, if the same frequency is present in more than one
> channel, phase will matter.
I think phase matters for mentally positioning the source of a sound,
too. I'm pretty sure that's one of the ways they make those "surround
sound headphones" and those "sounds like you're there" recordings.
--
Darren New / San Diego, CA, USA (PST)
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Darren New wrote:
> Orchid XP v8 wrote:
>> More significantly, if the same frequency is present in more than one
>> channel, phase will matter.
>
> I think phase matters for mentally positioning the source of a sound,
> too. I'm pretty sure that's one of the ways they make those "surround
> sound headphones" and those "sounds like you're there" recordings.
Oh, sure. But if you want that level of sound clarity, you're using
lossy audio compression...why? ;-)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> Oh, sure. But if you want that level of sound clarity, you're using
> lossy audio compression...why? ;-)
Just saying....
--
Darren New / San Diego, CA, USA (PST)
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On Tue, 04 Nov 2008 19:17:50 +0000, Orchid XP v8 wrote:
> Stephen wrote:
>
>> Why are we here?
>
> We're bored?
>
>> What is the meaning of 42?
>
> Would it be wrong to reply "4 * 10^2 + 2 * 10^2"? ;-)
Yes, because you've just described the number 600. ;-)
Jim
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> If the actual frequency falls in between two frequencies of the DFT,
> there's no way for the DFT to produce just one or a few lines.
Of course there is, try it. If you create a frequency that is half-way
between two frequencies in the DFT, your DFT histogram will still look the
same shape, the peak will just be shared between the two frequencies.
And of course if you analyse the DFT properly (ie not just look at a picture
of the magnitude of each result) you will be able to determine the exact
frequency. I mean in the worst case you can just do an inverse DFT to get
back the exact same signal!
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