Periodogram of a Multichannel Sound 

Pairs of frequencies used in a dual-tone multifrequency signaling (DTMF).

Create pairs of low and high frequencies for each key.

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X freqs = Flatten[Outer[List, {697, 770, 852, 941}, {1209, 1336, 1477}], 1]

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In[2]:=

X Grid[MapThread[ Prepend, {Prepend[ Partition[ MapIndexed[ Button[First[#2] /. {10 -> "*", 11 -> 0, 12 -> "#"}, (EmitSound[ Play[Sin[2 Pi #[[1]] t] + Sin[2 Pi #[[2]] t] + RandomReal[{-0.2, 0.2}], {t, 0, 0.2}]];), ImageSize -> {30, 30}] &, freqs], 3], Style[Quantity[#, "Hz"], Bold] & /@ {1209, 1336, 1477}], Prepend[Style[Quantity[#, "Hz"], Bold] & /@ {697, 770, 852, 941}, ""]}], Dividers -> {{False, True, False}, {False, True, False}}]

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Create a 12-channel sound combining tones of all 12 keys.

In[3]:=

X tones = Total[Sin[2 Pi # t] & /@ #] & /@ freqs

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In[4]:=

X snd = Sound[ SampledSoundList[Table[#, {t, 0, .3, 1/8000.}] & /@ tones, 8000]];

Visualize the periodogram of the created sound.

In[5]:=

X Periodogram[snd, ImageSize -> Medium]

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