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From: Vladimir Vassilevsky on 25 Jul 2010 08:47


Raeldor wrote:

> Hi Guys,
>
> I want to use FFT for an audio programming project I'm working on and
> had some (what are probably quite simple questions). I understand the
> concept that FFT converts a time based array of data into a frequency
> based array of data, and I found a nice library called FFTW which
> looks like it will fit the bill. My questions are...
>
> (These questions are based on an input array of 16-bit integers
> representing amplitude between -16,384 and 16,384, with a sample rate
> of 22k).
>
> 1. I understand with a 22k sample rate, my highest frequency is 10k,
> is that correct?
>
> 2. If I pass to the FFT routine a set of samples from this data with a
> length of 2048, I will get back 2048 values. a) Will the values still
> be in the range -16,384 to 16,384, and will they still represent
> amplitude? If so, how can a frequency have a negative amplitude...
> surely if the frequency is not present it should be zero. b) What
> frequency range will each returned sample represent and what are the
> upper and lower bounds of the entire returned set of data? Is this
> based on the number of samples I pass into the FFT function?
>
> Thanks
> Ray
From: VelociChicken on 26 Jul 2010 15:27


Troll:-

Subject: IMBECILE::Re: FFT Questions








>
>
> Raeldor wrote:
>
>> Hi Guys,
>>
>> I want to use FFT for an audio programming project I'm working on and
>> had some (what are probably quite simple questions). I understand the
>> concept that FFT converts a time based array of data into a frequency
>> based array of data, and I found a nice library called FFTW which
>> looks like it will fit the bill. My questions are...
>>
>> (These questions are based on an input array of 16-bit integers
>> representing amplitude between -16,384 and 16,384, with a sample rate
>> of 22k).
>>
>> 1. I understand with a 22k sample rate, my highest frequency is 10k,
>> is that correct?
>>
>> 2. If I pass to the FFT routine a set of samples from this data with a
>> length of 2048, I will get back 2048 values. a) Will the values still
>> be in the range -16,384 to 16,384, and will they still represent
>> amplitude? If so, how can a frequency have a negative amplitude...
>> surely if the frequency is not present it should be zero. b) What
>> frequency range will each returned sample represent and what are the
>> upper and lower bounds of the entire returned set of data? Is this
>> based on the number of samples I pass into the FFT function?
>>
>> Thanks
>> Ray


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