Frequency Testing

[Diceman83]

I was wondering if there are test tracks avaliable to test the frequency response of a sound system avaliable for free anywhere. I'd like to have tracks that are single tones of basic frequencies, and a couple that gradually increases the frequency from like 10 Hz to 25 kHz or so. I know that they exist somewhere, I'd just like to find something free. I had some of these a few years ago when I first had my computer speakers, but I can't find them anymore. What do people usually use when tuning their systems? My HU has a 7 band equalizer, which is pretty good for a lower end model like mine, so I'll be able to do a little without an external equalizer for now.

I'd also like to know what programs people use for analyzing the data coming from a mic in the car. Does it require special mics and computers, or can I use my walmart special computer mic and my laptop to do a spectrum analysis?

Thanks!

[AndonD454]

i think the realmofexcursion site has some sweeps, sine waves and songs.. not sure where else to fine em though

[sr20de4evr]

for tones:
http://www.resnet.trinity.edu/areyno...test_tones.zip

for rta (real time analyzing) you need a special mic and special software. The mics typically range from $80 to several hundred dollars, and there are a few free programs out there that you can use to analyze the results, but I'm not sure what they are. You would also want to use white or pink noise with that, not test tones.

[Diceman83]

Thanks sr20 and Andon! Ok, noob question... what's pink noise? I'm guessing white noise is mix of harmonic frequencies or something.

[sr20de4evr]

White noise can be thought of as 20,000 sine waves playing simultaneously, all at the same magnitude (one at each frequency in the audio spectrum). It sounds similar to when you turn an FM radio to a station that doesn't exist, or switch your tv to a channel that doesn't exist.

Pink noise is similar, except instead of each frequency playing at the same magnitude, each octave/decade/insert-other-logarithmically-scaled-step is playing at the same magnitude. It sounds similar to the sound of the ocean on a beach when it's calm.

Since with audio, each increase in "pitch" that we hear isn't a step of some set number, it's a percentage increase. Like for example, the difference between 50 and 100hz is MUCH MUCH bigger than the difference between 10,050 and 10,100hz. Even though in both cases it's a 50hz difference, the 50 to 100 jump is an entire octave increase and it sounds like a big difference to us, while the 10,050 to 10,100 jump probably wouldn't even be audible. Since with white noise each frequency is being played at the same magnitude, that means the range between 10k and 20k is being played at the same level as the range between 20 and 10k, even though 10k to 20k is only one octave and 20 to 10k is about 12 octaves. As a result it sounds very high pitched, since most of the sound is in the treble region. Pink noise sounds much smoother and more balanced since 50-100hz is being played at the same level as 100-200, and 200-400, and 10k-20k.

Both would work equally well for RTA purposes, the one you pick just depends on the mic and software that you use.

You can download them both online, though pink noise can be pretty hard to find. I think that you can also make pink noise if you run white noise through a 6dB/oct lowpass filter, but don't quote me on that.

[CBFryman]

there are 18,980 frequincies, thank you...
for individual sine waves?
Siggenny is a program that i have. its free. but for some reason when you try to turn a frequincy into a WMV or MP3 it cuts the frequincy by a whole octave and adds harmonics 1-2 octaves up. ie
20Hz makes
10Hz with 40-80Hz harmonics.

[sr20de4evr]

Originally Posted by CBFryman

there are 18,980 frequincies, thank you...

well, actually there are an infinite number of frequencies in that range, and white noise extends beyond 20 and 20k anyway, so yeah

[CBFryman]

ok whole number frequincies

[bumpinstang77]

umm no b/c frequency is more then just sound VERY high frequencies are light all the way up to like ultra violet rays...... and correct me if I'm wrong but isn't radiation a frequecy.

[Diceman83]

Um, you can't create light by making a speaker move back and forth really fast. Yes, light travels in a wave, and therefore has a frequency, but wavelength is what we use to measure light colors. The difference is that sound waves are a compression wave traveling through a medium (air), and any electromagnetic radiation (light, x-rays, infrared) is a particle moving in a wave pattern. Ok, enough of a physics lesson for today.

[ngsm13]

Originally Posted by Diceman83

Um, you can't create light by making a speaker move back and forth really fast. Yes, light travels in a wave, and therefore has a frequency, but wavelength is what we use to measure light colors. The difference is that sound waves are a compression wave traveling through a medium (air), and any electromagnetic radiation (light, x-rays, infrared) is a particle moving in a wave pattern. Ok, enough of a physics lesson for today.

Ha ha, just about to school Mike on that...he needs to study up in his physics class for EE.

And I honestly would say AN ORIGINAL CD copy is the best thing for pink noise. It shouldn't be a compressed file (i.e. mp3) I have it on my Bass Mekanik Power Tools 2.0 (2 cd Set). It's an amazing set, great for tuning, burping, all things. Look into, it's nice to have a REAL original CD quality hard copy. peace

NG

[bumpinstang77]

its still a frequency dammit..... just a uber high one

[CBFryman]

Audiable Frequincies. you also have inrasonic and supersonic frequincies by in car audio they dont matter. and the ecletromagnetic spectrum has nothing to do with audio... at extremely high ambient pressues we could make 100kHz but what would it matter? our eardrums cant even vibrate that fast... let alone the prussures needed to do that wouldnt be very comferatable....and it would take a long time to make your body equalize...

[bumpinstang77]

well SHIT DAMN

[Diceman83]

In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes:

NOTE: When waves travel from one medium to another, their frequency remains more or less the same - only their wavelength changes.

Speed of light is 299,792,458 meters per second and the wavelength of blue light is about 470 x 10^9 meters. The math puts it at 6.378 x 10^14 Hz. So yes, light has a very high frequency, but it's easier to deal with the wavelength because we can measure it.