Sirs, Few basic questions on DFT: 1) what is the signifiance of -ve amplitude in frequency domain 2) what is the significance when cosine component has -ve and sine has +ve amplitudes 3) In some literatures, the frequency domain is shown with magnitude and phase. Shouldn't this be magnitude and phase for real and imaginary parts (so totally 4 components)? 4) How is the energy calculated using Parseval's equation in the complex plane. Does it use real & imaginary and their phase counterparts for calculation also? 5) what is the purpose of windowing and whether this is done in time or frequency domain? Thanks, Manish
DFT & other basic questions
Started by ●October 13, 2012
Reply by ●October 14, 20122012-10-14
On 10/13/12 10:47 PM, manishp wrote:> Sirs, > > Few basic questions on DFT: > > 1) what is the signifiance of -ve amplitude in frequency domain > 2) what is the significance when cosine component has -ve and sine has +ve > amplitudesboy, my ignorance again slaps me in my face. i have no idea what "-ve" or "+ve" is. never read those terms before regarding the DFT.> 3) In some literatures, the frequency domain is shown with magnitude and > phase. Shouldn't this be magnitude and phase for real and imaginary parts > (so totally 4 components)?the phase of the imaginary part is always +90 degrees. the phase of the real part is 0.> 4) How is the energy calculated using Parseval's equation in the complex > plane.didn't know Parseval's theorem (this is that the energy in the frequency domain is equal to the energy in the time domain with a scaling factor tossed in depending on how the DFT definition is scaled) had much to do with the complex plane.> Does it use real& imaginary and their phase counterparts for > calculation also?it's magnitude-squared which is the same as real-squared plus imaginary-squared.> 5) what is the purpose of windowing and whether this is done in time or > frequency domain?the purpose is to taper the edges of the ends of the time-domain data set so that discontinuities are minimized and so the spurious frequency-domian components that are a result of this discontinuity are minimized. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●October 14, 20122012-10-14
robert bristow-johnson <rbj@audioimagination.com> writes:> i have no idea what "-ve" or "+ve" is. never read those terms before > regarding the DFT.negative/positive -- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com
Reply by ●October 16, 20122012-10-16
On Sunday, October 14, 2012 12:22:22 AM UTC-4, robert bristow-johnson wrote:> On 10/13/12 10:47 PM, manishp wrote: > > > Sirs, > > > > > > Few basic questions on DFT: > > > > > > 1) what is the signifiance of -ve amplitude in frequency domain > > > 2) what is the significance when cosine component has -ve and sine has +ve > > > amplitudes > > > > boy, my ignorance again slaps me in my face. > > > > i have no idea what "-ve" or "+ve" is. never read those terms before > > regarding the DFT. > > > > > 3) In some literatures, the frequency domain is shown with magnitude and > > > phase. Shouldn't this be magnitude and phase for real and imaginary parts > > > (so totally 4 components)? > > > > the phase of the imaginary part is always +90 degrees. the phase of the > > real part is 0. > > > > > 4) How is the energy calculated using Parseval's equation in the complex > > > plane. > > > > didn't know Parseval's theorem (this is that the energy in the frequency > > domain is equal to the energy in the time domain with a scaling factor > > tossed in depending on how the DFT definition is scaled) had much to do > > with the complex plane. > > > > > Does it use real& imaginary and their phase counterparts for > > > calculation also? > > > > it's magnitude-squared which is the same as real-squared plus > > imaginary-squared. > > > > > 5) what is the purpose of windowing and whether this is done in time or > > > frequency domain? > > > > the purpose is to taper the edges of the ends of the time-domain data > > set so that discontinuities are minimized and so the spurious > > frequency-domian components that are a result of this discontinuity are > > minimized. > > > > -- > > > > r b-j > > > > "Imagination is more important than knowledge."Robert, Parseval's is much more general than generally taught in DSP. It says if you have two functions g(t) and h(t) and their fourier transforms G(w) and H(w) that the integral of conj(g(t)) * h(t) dt = scalefactor* integral of conj(G(w))*H(w) dw. What most call Parseval's is really a special case where g(t) and h(t) are the same function. This is called Bessel's identity. Clay
Reply by ●October 21, 20122012-10-21
On Sun, 14 Oct 2012 11:00:49 -0400, Randy Yates <yates@digitalsignallabs.com> wrote:>robert bristow-johnson <rbj@audioimagination.com> writes: > >> i have no idea what "-ve" or "+ve" is. never read those terms before >> regarding the DFT. > >negative/positiveHi Randy, This a great example of laziness on the part of the original poster causing confusion for those trying to offer help. [-Rick-]
Reply by ●October 21, 20122012-10-21
Rick Lyons <R.Lyons@_BOGUS_ieee.org> writes:> On Sun, 14 Oct 2012 11:00:49 -0400, Randy Yates > <yates@digitalsignallabs.com> wrote: > >>robert bristow-johnson <rbj@audioimagination.com> writes: >> >>> i have no idea what "-ve" or "+ve" is. never read those terms before >>> regarding the DFT. >> >>negative/positive > Hi Randy, > This a great example of laziness on the part of the > original poster causing confusion for those trying > to offer help.I agree Rick. I try to avoid cutesie abbreviations in email and usenet for this reason. -- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com
Reply by ●October 21, 20122012-10-21
On 10/21/2012 11:30 AM, Rick Lyons wrote:> On Sun, 14 Oct 2012 11:00:49 -0400, Randy Yates > <yates@digitalsignallabs.com> wrote: > >> robert bristow-johnson <rbj@audioimagination.com> writes: >> >>> i have no idea what "-ve" or "+ve" is. never read those terms before >>> regarding the DFT. >> >> negative/positive > Hi Randy, > This a great example of laziness on the part of the > original poster causing confusion for those trying > to offer help. > > [-Rick-]We could put a stop to this by refusing to acknowledge posts that contain unreasonable abbreviations. We could wast the time by instead discussing at length which abbreviations were "reasonable" and which were not. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 22, 20122012-10-22
On Sun, 21 Oct 2012 08:30:08 -0700, Rick Lyons wrote:> On Sun, 14 Oct 2012 11:00:49 -0400, Randy Yates > <yates@digitalsignallabs.com> wrote: > >>robert bristow-johnson <rbj@audioimagination.com> writes: >> >>> i have no idea what "-ve" or "+ve" is. never read those terms before >>> regarding the DFT. >> >>negative/positive > Hi Randy, > This a great example of laziness on the part of the > original poster causing confusion for those trying to offer help.It must be an American thing; +ve and -ve are commonly used around here. Regards, Allan
Reply by ●October 23, 20122012-10-23
On 22 Oct 2012 10:08:21 GMT Allan Herriman <allanherriman@hotmail.com> wrote:> On Sun, 21 Oct 2012 08:30:08 -0700, Rick Lyons wrote: > > > On Sun, 14 Oct 2012 11:00:49 -0400, Randy Yates > > <yates@digitalsignallabs.com> wrote: > > > >>robert bristow-johnson <rbj@audioimagination.com> writes: > >> > >>> i have no idea what "-ve" or "+ve" is. never read those terms before > >>> regarding the DFT. > >> > >>negative/positive > > Hi Randy, > > This a great example of laziness on the part of the > > original poster causing confusion for those trying to offer help. > > > It must be an American thing; +ve and -ve are commonly used around here. > > Regards, > AllanAs a dirty colonial, I've never seen 'em before, and was wondering what the original poster's emitter voltages had to do with anything. -- Rob Gaddi, Highland Technology -- www.highlandtechnology.com Email address domain is currently out of order. See above to fix.
Reply by ●October 23, 20122012-10-23
On 22 Oct 2012 10:08:21 GMT, Allan Herriman <allanherriman@hotmail.com> wrote:>On Sun, 21 Oct 2012 08:30:08 -0700, Rick Lyons wrote: > >> On Sun, 14 Oct 2012 11:00:49 -0400, Randy Yates >> <yates@digitalsignallabs.com> wrote: >> >>>robert bristow-johnson <rbj@audioimagination.com> writes: >>> >>>> i have no idea what "-ve" or "+ve" is. never read those terms before >>>> regarding the DFT. >>> >>>negative/positive >> Hi Randy, >> This a great example of laziness on the part of the >> original poster causing confusion for those trying to offer help. > > >It must be an American thing; +ve and -ve are commonly used around here. > >Regards, >AllanHi Allan, Ah ha. That explains things. I don't recall ever seeing "+ve" and "-ve" before. Does "around here" mean the place where people can "open the boot" of their cars? [-Rick-]
