Path: utzoo!attcan!uunet!microsoft!brianw From: brianw@microsoft.UUCP (Brian Willoughby) Newsgroups: comp.dsp Subject: Re: FFT / FHT (was Re: Adjust-Speed CD player?) Summary: FHT not for HiFi? Keywords: Hartley Fourier Message-ID: <7925@microsoft.UUCP> Date: 2 Oct 89 02:21:19 GMT References: <698@lakart.UUCP> <10471@csli.Stanford.EDU> Reply-To: brianw@microsoft.UUCP (Brian Willoughby) Organization: Microsoft Corp., Redmond WA Lines: 25 In article <10471@csli.Stanford.EDU> poser@csli.stanford.edu (Bill Poser) writes: >The Fast Hartley Transform is described in great detail in >Ronald Bracewell's recent book _The Hartley Transform_. Mathematically, >the Hartley transform is like the Fourier Transform but has a real >kernel, that is, cos + sin instead of cos + i sin. It is therefore not >the same as the Fourier Transform. However, the MAGNITUDE of the >Hartley Transform is the same as that of the Fourier Transform. In the >many cases in which one only cares about the magnitude, not the phase, >the Fourier Transform may be replaced by the Hartley transform. For use in a one-way transform - perhaps to display frequency spectrum content of audio data - the FHT might be the choice. But, since HiFi audio is often discussed in this group, I wanted to point out that the phase information is necessary to accurately reconstruct the original signal. If the goal is to process the frequency domain data obtained from a Fourier Transform and then reconstruct a modified version of the original time domain data, it follows that a great deal of information would be lost without the phase of each frequency component. Brian Willoughby UUCP: ...!{tikal, sun, uunet, elwood}!microsoft!brianw InterNet: microsoft!brianw@uunet.UU.NET or: microsoft!brianw@Sun.COM Bitnet brianw@microsoft.UUCP