Hi, I'm looking to recreate an audio environment for a flight simulator. I've been supplied with a document that contains different flight conditions (eg, plane at idle, plane during takeoff, climb from 15000 to 35000ft, etc) as well as the location (in the plane) of the recorders for these conditions. This document also contains an Octave band (or narrow band, depending on the condition) analysis of each condition. I'm somewhat familiar with signal processing and frequency spectrum analysis, but this is the first time I've encountered Octave band analysis. What i would like to do is to create a wave file based on this data and hopefully be able to play back the sound this data represents (in any media player). My question is on how to interpret the data. The plots are sound level (dB) vs time (seconds), and there are plots for various center frequncies (can you define this term?): 63Hz, 125Hz, 250Hz, 500Hz......up to 8000Hz. If i were to determine the time domain equvalent of each plot, and generate their sine waves, mix them and write the output to file, would that essentially recreate the sound for a particular condition? My intuition tells me that there is more to it than that, as these center frequencies don't seem to represent the entire frequency spectrum of a given condition. Can I also be pointed to an online resource that may give me a better understanding of Octave band analysis? My background is Computer Engineer, software, but I think i understand the fundamentals of signal processing (ie a first course in signals and systems), so I don't want anything too basic, but not too advanced either. Any help is very welcome. Thanks in advance. David Reid
Time-Domain, FFT, and Octave (and 1/3 Octave) band analysis
Started by ●February 19, 2004
Reply by ●February 19, 20042004-02-19
"David Reid" <no_spam@mechtronix.ca> wrote in message news:ou4Zb.6610$w65.610499@news20.bellglobal.com...> Hi, > > I'm looking to recreate an audio environment for a flight simulator. I've > been supplied with a document that contains different flight conditions(eg,> plane at idle, plane during takeoff, climb from 15000 to 35000ft, etc) as > well as the location (in the plane) of the recorders for these conditions. > This document also contains an Octave band (or narrow band, depending onthe> condition) analysis of each condition. I'm somewhat familiar with signal > processing and frequency spectrum analysis, but this is the first timeI've> encountered Octave band analysis. What i would like to do is to create a > wave file based on this data and hopefully be able to play back the sound > this data represents (in any media player).David, I suggest you use Google Groups on comp.dsp - we've had a few discussions about how to do this sort of thing.>What i would like to do is to create a > wave file based on this data and hopefully be able to play back the sound > this data represents (in any media player).Hmmmmm.... the only thing you'd be able to do with octave band levels would be to generate noise at the proper levels in each band - and possibly further smooth the spectral density curve as part of the process. Any tonal information you wouldn't know / have .. in order to go backwards from octave levels. Is that what you want? Fred
Reply by ●February 19, 20042004-02-19
Yes, that answers my question. Thanks, I'll search comp.dsp for more info. David Reid "Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message news:eeGdncAMZ6t6n6jdRVn-hQ@centurytel.net...> > "David Reid" <no_spam@mechtronix.ca> wrote in message > news:ou4Zb.6610$w65.610499@news20.bellglobal.com... > > Hi, > > > > I'm looking to recreate an audio environment for a flight simulator.I've> > been supplied with a document that contains different flight conditions > (eg, > > plane at idle, plane during takeoff, climb from 15000 to 35000ft, etc)as> > well as the location (in the plane) of the recorders for theseconditions.> > This document also contains an Octave band (or narrow band, depending on > the > > condition) analysis of each condition. I'm somewhat familiar withsignal> > processing and frequency spectrum analysis, but this is the first time > I've > > encountered Octave band analysis. What i would like to do is to createa> > wave file based on this data and hopefully be able to play back thesound> > this data represents (in any media player). > > David, > > I suggest you use Google Groups on comp.dsp - we've had a few discussions > about how to do this sort of thing. > > >What i would like to do is to create a > > wave file based on this data and hopefully be able to play back thesound> > this data represents (in any media player). > > Hmmmmm.... the only thing you'd be able to do with octave band levelswould> be to generate noise at the proper levels in each band - and possibly > further smooth the spectral density curve as part of the process. Anytonal> information you wouldn't know / have .. in order to go backwards fromoctave> levels. Is that what you want? > > Fred > >
Reply by ●February 19, 20042004-02-19
To refine my question, based on your reply and new info.... I noticed at the end of the document that there is indeed the full spectrum but for certain conditions only. If i understand you correctly, if i took one of the base conditions with the full spectrum (eg, engines at cruise at 5000ft), i could use the octave band plots (of lets say, climb from 5000ft to 35000ft over 60 secs) to adjust the full spectrum at the different center freq's of the octave plots to get the full spectrum of the latter condition? I hope i made that clear... David Reid "Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message news:eeGdncAMZ6t6n6jdRVn-hQ@centurytel.net...> > "David Reid" <no_spam@mechtronix.ca> wrote in message > news:ou4Zb.6610$w65.610499@news20.bellglobal.com... > > Hi, > > > > I'm looking to recreate an audio environment for a flight simulator.I've> > been supplied with a document that contains different flight conditions > (eg, > > plane at idle, plane during takeoff, climb from 15000 to 35000ft, etc)as> > well as the location (in the plane) of the recorders for theseconditions.> > This document also contains an Octave band (or narrow band, depending on > the > > condition) analysis of each condition. I'm somewhat familiar withsignal> > processing and frequency spectrum analysis, but this is the first time > I've > > encountered Octave band analysis. What i would like to do is to createa> > wave file based on this data and hopefully be able to play back thesound> > this data represents (in any media player). > > David, > > I suggest you use Google Groups on comp.dsp - we've had a few discussions > about how to do this sort of thing. > > >What i would like to do is to create a > > wave file based on this data and hopefully be able to play back thesound> > this data represents (in any media player). > > Hmmmmm.... the only thing you'd be able to do with octave band levelswould> be to generate noise at the proper levels in each band - and possibly > further smooth the spectral density curve as part of the process. Anytonal> information you wouldn't know / have .. in order to go backwards fromoctave> levels. Is that what you want? > > Fred > >
Reply by ●February 20, 20042004-02-20
"David Reid" <no_spam@mechtronix.ca> wrote in message news:1E8Zb.6857$w65.627280@news20.bellglobal.com...> To refine my question, based on your reply and new info.... > > I noticed at the end of the document that there is indeed the fullspectrum> but for certain conditions only. If i understand you correctly, if i took > one of the base conditions with the full spectrum (eg, engines at cruiseat> 5000ft), i could use the octave band plots (of lets say, climb from 5000ft > to 35000ft over 60 secs) to adjust the full spectrum at the differentcenter> freq's of the octave plots to get the full spectrum of the lattercondition?> > I hope i made that clear...David, I think it's a lot more complicated than that. I don't know how you "build" a sound from such little information unless it is almost purely colored (i.e. not flat spectral density) noise. If it's just colored broadband noise then maybe.... However, my experience is that noise often has considerable tonal and harmonic constituents of import. These you don't seem to have a model for. For example, the engines may increase in frequency (rpm) during climb but reduce once more after the climb. At the same time, pumps may turn off and on and off again and some pumps may simply run at the same speed all the time. etc. etc. Now *that's* complicated and probably untenable. I used to construct unending sound "loops" from actual recordings - and *that* was hard. Fred
Reply by ●February 20, 20042004-02-20
Well that's more like what i'll be doing, building loops from recordings. I was just wondering about the theory behind what I previously mentioned. The sample model that you have mentioned is pretty much the kind of thing that we'll be doing. The document mentioned contains octave band analysis for such a condition and others (too many to mention) and our goal is to build a model based on all the data. The final implemenation in the simulator (ie, sounds coming out of all of the speakers) will be measured with a spectrum analyser and the output has to match what was contained in the document. But i think our problem is the lack of a dsp expert. As things become clearer, I'll post more questions. Thanks for the replies, they're very helpful. David Reid "Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message news:WZ-dnYrJkbFGP6jd4p2dnA@centurytel.net...> > "David Reid" <no_spam@mechtronix.ca> wrote in message > news:1E8Zb.6857$w65.627280@news20.bellglobal.com... > > To refine my question, based on your reply and new info.... > > > > I noticed at the end of the document that there is indeed the full > spectrum > > but for certain conditions only. If i understand you correctly, if itook> > one of the base conditions with the full spectrum (eg, engines at cruise > at > > 5000ft), i could use the octave band plots (of lets say, climb from5000ft> > to 35000ft over 60 secs) to adjust the full spectrum at the different > center > > freq's of the octave plots to get the full spectrum of the latter > condition? > > > > I hope i made that clear... > > David, > > I think it's a lot more complicated than that. I don't know how you"build"> a sound from such little information unless it is almost purely colored > (i.e. not flat spectral density) noise. If it's just colored broadband > noise then maybe.... > > However, my experience is that noise often has considerable tonal and > harmonic constituents of import. These you don't seem to have a modelfor.> For example, the engines may increase in frequency (rpm) during climb but > reduce once more after the climb. At the same time, pumps may turn offand> on and off again and some pumps may simply run at the same speed all the > time. etc. etc. Now *that's* complicated and probably untenable. > > I used to construct unending sound "loops" from actual recordings - and > *that* was hard. > > Fred > >