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On Tue, 10 Feb 1998 11:56:18 -0500 (EST), John Kim wrote: >On Mon, 9 Feb 1998, Paul Khoury wrote: >> On Mon, 09 Feb 1998 17:06:15 -0700 (MST), billy@MIX.COM wrote: >> >> >> >22kHz is a bit high for a 44.1kHz sampling rate - the high frequency >> >> >limit is one half the sampling rate... >> >> > >> >> I don't quite understand (for a change. <g> ). Could you explain that >> >> again, please? >> > >> >In the world of digital sound recording and transmission there is >> >what's called (I believe) Shannon's law (many years since I was in > >I always thought it was Nyquist's theorem. Shannon is usually >more associated with coding information inside a signal. > >> >school) which says the highest frequency that can be digitized is >> >one-half the digital sampling rate. Thus a 44.1kHz sample rate >> >system can only go up to 22.05kHz. Then there are anti-aliasing >> >low-pass filters to enforce this, but they are not perfect so there's >> >some gradual decline in frequency response before hitting the actual >> >cutoff point. Since in this case you are only 50Hz away in practice >> >there will not be much left of your signal after going through this >> >filter. >> > >> >For what it's worth any decent analog tape recorder running at >> >15 ips (inches per second) or faster would record this quite well. >> >Or if you could sample at 48kHz you might have a chance of getting >> >it that way too. I don't know what software might be available >> >for the Thinkpad at that sample rate though. > >I believe the default DOS audio software that came with the 701 >is capable of 48kHz. It's been ages since I booted to DOS so I >could be wrong. > Same here. I'm only using OS/2, so that's currently my only option for recording. >> >The next step in commercial systems looks like a 96kHz sample >> >rate - if this eventually finds its way into notebook computers >> >you'd have no trouble at all, but that's probably a year or >> >two away. >> >> I'm just trying to record a train passing by for a small project, >> so if I choose 22KHz, is that the sample rate, or the other rate? >> >> Or do you think 11KHz might work fine as well? > >That depends on what you want to record. If it's just an audio >effect or looking at a doppler shift, 22kHz (44kHz sampling >rate) is above the hearing range for most people (depending on >age and gender, most people limit out at around 14kHz to 20kHz). >If you've never heard a 16-20kHz sound, it is *very* high >pitched. 22kHz sampling should be fine. You may even be able >to get away with 11kHz (depending on if you're listening for the >whistle or the engine roar). > >OTOH, if you want to do a sophisticated analysis of the sound of >a train passing, you're going to need the higher frequencies a >44, 48, or 96kHZ sampling rate will provide. The fundamental >tone of any sound (e.g. a whistle) is its lowest frequency. All >the harmonics and overtones that give each different sound its >individual character are higher in frequency, often several >octaves (one octave is twice the frequency). Also oversampling >makes it easier to run a Fourier transform (to get it into >frequency space so you can tell which "notes" make up the whole >thing). > >Boy does this bring back memories... :-) Just wondering, what do you do for a living? This is getting quite interesting. :) (Of course, I'm only 18, so I have a long ways to go to get MORE knowledge :) ). And the project is mainly to get a sound for an alarm clock I'd like to program (as soon as I figgure out how to program in C). -- Paul Khoury <pkhoury@loop.com> http://pkhoury.dyn.ml.org (If you get an error, then the server is not online) Current system statistics: The Operating System/2 Version is 4.00 Revision 9.029 There are 22 Processes with 83 Threads. This machine's uptime is 0d 22h 35m 54s 640ms.