Re: noise_table question

Hi all,
I have updated the document to reflect the frequencies must be ascending 
and unique.

"Noise pairs are specified in the order of ascending frequencies and 
each frequency value must be unique."

Cheers...
Dave

Geoffrey.Coram wrote:
> Paul -
> I think you're correct that this ought to be clarified, that
> the frequencies should be strictly greater than the previous.
>
> I could imagine that someone might think to create a 
> discontinuous interpolation by specifying
> { 1,5, 10,5, 10,1, 1e3,1 }
> such that one gets 5 on the interval [1,10) and
> 1 on the interval [10,1e3].  However, 
> a) the value at 10 is ambiguous
> b) noise probably shouldn't be discontinuous like this
> c) one can still get arbitrarily close to this by
> specifying { 1,5, 10,5, 10.0000001,1, 1e3,1 }
> and satisfy the new requirement.
>
> -Geoffrey
>
>
> Paul Floyd wrote:
>   
>> In the 2.2 LRM, Section 4.5.4.3 it says
>>
>> /"The noise_table() function interpolates a vector to model a process
>> where the spectral
>> density of the noise varies as a piecewise linear function of frequency.
>> The general form
>> is
>> noise_table( vector [ , name ] )
>> where vector contains pairs of real numbers: the first number in each
>> pair is the
>> frequency in Hertz and the second is the power. Noise pairs are
>> specified in the order of
>> ascending frequencies. noise_table() performs piecewise linear
>> interpolation to compute
>> the power spectral density generated by the function at each frequency."/
>>
>> It's not entirely clear to me that each frequency must be greater than
>> the previous one (as opposed to greater than or equal). If "greater than
>> or equal" were permitted, then it would introduce the posibility of two
>> frequencies having different power levels, which would make the
>> interpolation ambiguous. Clearly this is not the intent.
>>
>> Do you think that it is worth changing the wording to make it explicit
>> that no duplicate frequencies are allowed?
>>
>> Regards
>> Paul
>>     
>
>   


-- 
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-- David Miller
-- Design Technology (Austin)
-- Freescale Semiconductor
-- Ph : 512 996-7377 Fax: x7755
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