Customizing output of Spectrogram[], units of Periodogram[]?

Question

I am analyzing spectrum of recorded sound. For that purpose I am using Mathematica's built in functions Spectrogram[] and Periodogram[]. I have three questions regarding those:

1. What is the way to set desired range on frequency axis (y-axis) in Spectrogram[]'s output, so that it "zooms in" to frequencies at specific interval? I managed to accomplish this with Show[], but it removes my x axis ticks.

2. How to change tick positions on frequency axis (so for example that I have them every 200 Hz)?

3. Regarding the Periodogram[] function, what y axis represents (what are the units)?

It seems to me like something in decibels, I looked in MMA's documentation, searched on internet, and I couldn't find answer. Documentation says:

plots the squared magnitude of the discrete Fourier transform (power spectrum) of list

And I understand that the periodogram tells me which frequency is most present. But what are the units?

Thank you for any helpful answers, comments or advices...

Answer 1

You can zoom in; just use PlotRange ( I have combined the tick specification and zooming-in in one plot)

Spectrogram[data, 64, 2, BlackmanHarrisWindow, ImageSize -> 500,  ImageMargins -> 10,
     SampleRate -> 483, PlotRange -> All]

ticksY = Reverse@Transpose[{30 #1, 10 #1}]& @ Range@7
ticksX = Transpose[{.25 #1, .25 #1}]& @ Range@4
Spectrogram[data, 64, 2, BlackmanHarrisWindow, ImageSize -> 500, ImageMargins -> 10,
     SampleRate -> 483, PlotRange -> {All, {10, 100}}, FrameTicks -> {ticksY, ticksX}]

As for the Periodogram, read under Properties & Relations. The example is the following

data = Table[2 Sin[0.2 π n] + Sin[0.5 π n] + RandomReal[{-1, 1}], {n, 0, 127}];
{Periodogram[data], ListLinePlot[Take[20 Log[10, Abs[Fourier[data]]], 64]]}

Now, there is a relationship that states $10\; log_{10}(\frac{v^{2}}{w^{2}}) = 20\; log_{10}(\frac{v}{w})$ Great; Let's put that to the test !

{Periodogram[data], ListLinePlot[Take[10 Log[10, Abs[Fourier[data]]^2], 64]]}]

So, they are the same thing and the units are dB