travis@bsu-cs.bsu.edu (Travis Michael Banks) (12/17/90)
Can someone please tell me what WHITE NOISE is? I've seen it referred to on several occasions and have no idea what it is??? Please Email me and let me know thanks -Travis -- email: travis@bsu-cs.bsu.edu Disclaimer: The opinions expressed above do not represent the opinions of my employer. Of course Ronald McDonald doesn't know much about MIDI though!
seaotter@athena.mit.edu (12/17/90)
travis@bsu-cs.bsu.edu (Travis Michael Banks) writes: > >Can someone please tell me what WHITE NOISE is? >I've seen it referred to on several occasions and have no idea what it is??? A song by Jay Ferguson from some years ago ... ;-) Ciao, Mike -- | Mike Zraly | You should never wear your best trousers | | (mzraly@ldbvax.dnet.lotus.com) | when you go out to fight for freedom and | | via: seaotter@athena.mit.edu | liberty. -- Henrick Ibson |
mpmst1@unix.cis.pitt.edu (metlay) (12/17/90)
In article <12263@bsu-cs.bsu.edu> travis@bsu-cs.bsu.edu (Travis Michael Banks) writes: > >Can someone please tell me what WHITE NOISE is? >I've seen it referred to on several occasions and have no idea what it is??? White noise is a kind of audio signal where each frequency is represented with an equal amount of power.... it's "white" in the same way that light from the Sun, containing all frequencies of the EM spectrum, is perceived as white by our eyes. (I know sunlight isn't an equal-power source. shut up) Alternatives are types of noise where power output is weighted with respect to frequency: the best known example in our field, used for testing rooms for mic placement as well as on the better analog synths, is pink noise, which follows a frequency dependence considered more interesting to the human ear. Its dependence is a very simple math formula involving one over the frequency, but I don't dare try to quote it from memory or the zillions of net.nit.pickers out there will leap on me like hyenas. Other types of noise include blue, red, and green (blue noise is weighted toward the high end, red toward the low, and green noise is that far-off sound of lawn mowers that wakes you up when you're trying to take an afternoon nap in the summertime). Hope that helps. Someone else can show off their library by quoting you the math; on a practical level, what matters is that white noise is what you normally get on a synth that provides noise at all-- which is a pity, as pink noise is much more interesting to the ear. *sigh* Have a good holiday season, everyone. -- metlay | "There's more to life than marriage, metlay@vms.cis.pitt.edu | synths, and Traveller...but so what?"
mgresham@artsnet.UUCP (Mark Gresham) (12/18/90)
In article <12263@bsu-cs.bsu.edu> travis@bsu-cs.bsu.edu (Travis Michael Banks) writes: > >Can someone please tell me what WHITE NOISE is? Mid-western avant-garde music. :-) Cheers, --Mark ======================================== Mark Gresham ARTSNET Norcross, GA, USA E-mail: ...gatech!artsnet!mgresham or: artsnet!mgresham@gatech.edu ========================================
alex@bilver.uucp (Alex Matulich) (12/18/90)
In article <71303@unix.cis.pitt.edu> mpmst1@unix.cis.pitt.edu (metlay) writes: >In article <12263@bsu-cs.bsu.edu> travis@bsu-cs.bsu.edu (Travis Michael Banks) writes: >> >>Can someone please tell me what WHITE NOISE is? >>I've seen it referred to on several occasions and have no idea what it is??? > >White noise is a kind of audio signal where each frequency is represented >with an equal amount of power.... it's "white" in the same way that light >[...] >Alternatives are types of noise where power output is weighted with respect >to frequency: the best known example in our field, used for testing rooms >for mic placement as well as on the better analog synths, is pink noise, >which follows a frequency dependence considered more interesting to the >human ear. Its dependence is a very simple math formula involving one over >the frequency, but I don't dare try to quote it from memory or the zillions Actually, the simplest definition of pink noise is a signal composed of all frequencies, weighted in such a way that there is equal energy in every octave, rather than equal energy at every frequency in the case of white noise. Pink noise is generally used for testing audio equipment because it won't blow your tweeters at high volume levels like white noise can. For example, say you have two speakers, one designed to respond between 500-1000 Hz, and another designed to respond between 10,000-20,000 Hz. Each speaker has a response range of one octave. But look how many more "Hertzes" there are in the higher octave! Sending white noise to the higher-range speaker will result in 20 times more power being sent to it than the lower-range speaker! Using pink noise would cause equal power to be transmitted by each speaker in this example. -- _ |__ Alex Matulich (alex@bilver.UUCP) /(+__> Unicorn Research Corp, 4621 N Landmark Dr, Orlando, FL 32817 //| \ UUCP: ...uunet!tarpit!bilver!alex ///__) bitnet: IN%"bilver!alex@uunet.uu.net"
jmuller@Stardent.COM (Jim Muller) (12/19/90)
In <12263@bsu-cs.bsu.edu> travis@bsu-cs.bsu.edu (Travis Michael Banks) writes: >Can someone please tell me what WHITE NOISE is? I see that metlay wrote a description that also mentioned pink noise. His explanation is okay but contains a few "imprecisions", well, okay, technical inaccuracies. I like the green noise description though... :-) (Neither white nor pink noise definitions have anything to do with the human ear.) White noise is noise, actually *any* time signal, in which the power per frequency is constant. In continuous space (i.e. calculus), this means dP/dF = k. In discrete space, such as time measurements of voltage (you can use either amplitude, e.g. voltage, or power), analyzed via FFT, this means a constant power (or constant amplitude) for all frequencies, given a fixed delta-F. More properly, we should speak of the expected value, with a given distribution of sampling variation, since we usually mean random, aperiodic, non-deteministic noise. At any given time, the amplitude has only one value, of course. A "spectrum", be it discrete FFT or continuous via analytical Fourier Transform, is a time-integral, and thus assumes a time-window over which that "spectrum" applies. We rarely have a complete time history over which to calculate a spectrum, and in music, we never do. However, we can calculate a spectrum over a time interval, then do it again and again, forming a time-dependent spectrum. This is valid provided there is enough time in the interval to cover the frequencies desired, and that there be enough overlap (in time) of successive calculations, typically a factor of 2. With less overlap, there is a possibility of aliasing of the high frequencies to appear to have pulsating amplitudes. This is generally not an issue with musical applications, and probably is rarely considered. The net result is that we generally speak of the power per frequency being constant, but in reality we mean: If we measure it over a number of time intervals, and if the noise is more or less "constant", we will see variation with time but the mean value will be constant over time and over frequency. The constant-over- time part is assumed anyway, with "mean value" being explicit when we say "is constant". What makes it "white" is the constant-over-frequency part. So it is a simplification, but a reasonable one, to say dP/dF = k. So what then is "pink" noise? How does it differ from white and what is it used for? Pink noise is a similer aperiodic noise, but with the frequency distribution different. It has a decrease in power of 3dB per octave; more precisely, the power at 2f is 1/2 of that at f. Why use such a power distribution? In musical applications, we are usually concerned with octaves, i.e. frequency bands which get wider as you go up. We speak of 30-60Hz, 60-125Hz, 125-250Hz, 250-500Hz, etc. If we used equal-width frequency intervals like those produced by an FFT, or as appropriate for white noise, we would need twice as many intervals for 60-125Hz as for 30-60Hz, and twice as many again for 125-250Hz, etc. To avoid this overload, we use a logarithmic frequency scale. But if you analyze and display the time-dependent spectrum of white noise on a scale in which the frequency intervals get wider with increasing frequency, the apparant power in each band will go up by a factor of two for each band. What is "flat" on a linear frequency scale is ramped up with frequency on this logarithmic scale. So we just start with a noise that has a power reduction of a factor of two for every increase of that much in frequency, i.e. P = k/f. This way, it looks "flat" when analyzed and displayed on a typical music-oriented octave-based frequency scale. It has nothing to do with the human ear. It is simple math... Just what you didn't really wnat to know... -- - Jim Muller
e85rw@efd.lth.se (Ricard Wolf) (12/20/90)
In article <71303@unix.cis.pitt.edu> mpmst1@unix.cis.pitt.edu (metlay) writes: >In article <12263@bsu-cs.bsu.edu> travis@bsu-cs.bsu.edu (Travis Michael Banks) writes: [ .. nice description of various noise forms .. ] >Hope that helps. Someone else can show off their library by quoting you the >math; on a practical level, what matters is that white noise is what you >normally get on a synth that provides noise at all-- which is a pity, as >pink noise is much more interesting to the ear. *sigh* It may be more interesting to the ear, but not to the synthesiser player! :-) Seriously though, most analog synthesisers only have lowpass filters, so the only thing you can do with the noise is filter away the high end, and when it comes to pink noise, there isn't a lot of high end around to start with. I actually remember using an old PAiA Gnome for a noise source at one point, since I could set it's (rather mediocre) bandpass filter to give a sharp, cutting noise soumd, which could then be processed by my main synthesiser. (Yeah, we know, Metlay, that some people have Xpanders with multiple multimode filters etc, but some of us have to do with a simple Moog 24dB lowpass... :-). -- Ricard Wolf +--------------------------+-------------------------------------+ | Ricard Wolf | Lund Institute of Technology | | email: e85rw@efd.lth.se | If you can't buy 'em - build 'em !! | +--------------------------+-------------------------------------+
davet@cbnewsj.att.com (Dave Tutelman) (12/22/90)
In article <1990Dec17.224535.23225@bilver.uucp>, alex@bilver.uucp (Alex Matulich) writes: > > Actually, the simplest definition of pink noise is a signal composed of > all frequencies, weighted in such a way that there is equal energy > in every octave, rather than equal energy at every frequency in the > case of white noise. > > Pink noise is generally used for testing audio equipment because it > won't blow your tweeters at high volume levels like white noise can. Alex, Good definition, good example. Another use I've seen for pink noise in audio systems is in the use of an equalizer to correct for room acoustics. Equalizers and audio spectrum analyzers tend to have their sliders (or display bars) arranged by octaves (or n-per-octave) rather than absolute frequency, so pink noise is better matched than white. In fact, what you want is to adjust the equalizer so that the spectrum analyzer has all bars the same height. This indicates equal power in each fraction-of-an-octave, which is the same as the pink noise in. If you used white noise for this exercise, you'd have to match to an exponential response on the spectrum analyzer, much harder than a simple "all bars the same height." You'd also need a spectrum analyzer capable of accurately measuring and displaying very different powers simultaneously in different bands. Dave +---------------------------------------------------------------+ | Dave Tutelman | | Physical - AT&T Bell Labs - Lincroft, NJ | | Logical - ...att!pegasus!dmt == dmt@pegasus.att.com | | Audible - (201) 576 2194 | +---------------------------------------------------------------+