What?! No 'Chirp' function in MMA? Here you go...

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What?! No 'Chirp' function in MMA? Here you go...

Postby telefunkenvf14 » Fri Jul 02, 2010 9:18 pm

I posted this on MathGroup and figured someone here might find it useful as well.

----------------------------------

Group:

A while back I needed an exponential chirp function and was only able to track down a linear version by Will Robertson. Hopefully someone will find these useful.

linearChirp::usage = "linearChirp[f0_, f1_, t_, T_] generates a linear chirp signal with initial frequency f0 and ending frequency f1 at time T seconds; t represents the time index variable."

expChirp::usage = "expChirp[f0_, f1_, t_, T_] generates an exponential chirp signal with initial frequency f0 and ending frequency f1 at time T seconds; t represents the time index variable."

Attributes[linearChirp] = {NumericFunction}
linearChirp[f0_, f1_, t_, T_] :=Sin[2*Pi*t*(f0 + ((f1 - f0)/T*t)/2)]

Attributes[expChirp] = {NumericFunction}
expChirp[f0_, f1_, t_, T_] :=Sin[(2*f0*(-1 + (f1/f0)^(t/T))*Pi*T)/Log[f1/f0]]

--------------- Example Uses------------------
(*Just gives you the function; plug a value in for t to get the function value*)
linearChirp[10, 30, t, 1]

(*Compare plots... change the 10 to a 1 to see more of a difference*)
Plot[linearChirp[10, 30, t, 1], {t, 0, 1}]
Plot[expChirp[10, 30, t, 1], {t, 0, 1}]

(*Create a 40 second expChirp with starting frequency 20Hz, ending frequency 400Hz. Evaluate[] forces the function to evaluate first---speeds things up. Note that SampleDepth and SampleRate are overkill for this example; my goal was to avoid digital shenanigans later.*)

Play[Evaluate@expChirp[20, 400, t, 40], {t, 0, 40}, SampleDepth -> 24, SampleRate -> 44100]]

-RG
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