# How can I find the actual frequency given a normalized frequency?

Suppose that we have some sample:

y =

31.2241
-5.9830
22.6058
-2.2309
-42.8272
29.2850
-6.2652
20.8502
-2.4639
-44.7525
30.1104
-6.0180
21.4476
-1.5089
-45.1826
29.2744


and somehow I know that it is obtained via a sinusoidal method which contains two sine functions at different frequencies and amplitudes, so I apply the music method:

pmusic(y,4)


and obtain the plot:

I know the location of peaks at the normalized peaks, but I don't know the actual frequency. How can I find it?

I know the formula is $\frac{\text{normalized frequency}*f_s}{2}$, but what about $f_s$? Can I find it?

[Y,FS,NBITS]=wavread(FILE) returns the sample rate (FS) in Hz and the number of bits per sample (NBITS) used to encode the data in the music file.

After that, [S,F] = pmusic(Y,4,F,FS) to compute the pseudospectrum at frequencies F in Hz.

• but what is file?and what is inside it?
– user350
Feb 16, 2014 at 16:42
• actualy i want to find frequency,not indicate myself
– user350
Feb 16, 2014 at 16:43
• how do you get the original data y? You cannot get any information directly from an arbitrary given vector. I thought you sampled the data from a music file or something. Feb 16, 2014 at 16:45
• no i have some date,which is given at some frequency,but in real live should i know sampled frequency?
– user350
Feb 16, 2014 at 16:54
• suppose that that is signal coming from somewhere with additive noise,then what should i do?
– user350
Feb 16, 2014 at 16:58