Path: utzoo!attcan!uunet!husc6!bloom-beacon!apple!bionet!ig!relph From: relph@presto.ig.com (John M. Relph) Newsgroups: comp.sys.next Subject: Re: Fwd: LSC problem Message-ID: <6840@ig.ig.com> Date: 16 Nov 88 01:20:56 GMT References: Reply-To: relph@PRESTO.IG.COM.UUCP (John M. Relph) Organization: IntelliGenetics Inc., Mtn. View, Ca. Lines: 28 In article fry%zariski@harvard.harvard.edu (David Fry) writes: >For those who don't know, systems are being developed that >can do a Fourier analysis of repeated sounds to find their >component sound waves, and then emit a sound composed of the >the mirror image of these waves, resulting in destructive >interference. Your ear then hears nothing. This could be >used in an airplane, for instance, so the passengers would >hear no engine noise. > >With its built-in digitizer, its sound generation >capabilities, and its powerful DSP chip for Fourier analysis, >it seems that it would be pretty simple for the NeXT to do >this in real time. I don't think the NeXT machine is up to doing this. In the physics demo where voice was being analysed real-time and frequency plots being displayed, it seemed to be able to do a display every second (perhaps slightly faster or slower). Perhaps, with repeated sounds, this is fast enough to keep the generated "mirror-image" sounds in sync, but I don't think so. It would seem that, for example, if the engine was slowing, the "mirror-image" sound would always be a few Hz higher than the actual engine noise, resulting in a non-zero interference sound. This could be real nasty. In some situations this might actually result in louder noise. Ouch. But then again, perhaps not. -- John