# Matlab audio signal through audiometer

I am very new to audio processing and I am using matlab to produce a signal to be presented through an audiometer.

The way I am doing it is as follows:

1) Set the dB amplitude level in my GUI to 0dB (I have been told to use 0dB as the max and anything below to reduce the levels and not go above 0dB)

2) Use the audiometer to calibrate it such that the dB I read on the dB meter is 80dB

Now if I want to reduce the dB level by 6dB so now the input is -6dB, the reading on the meter is more like 78dB ish and not 74dB as I expected.

Why is that so?

The code I am using is as follows:

Fs = 16000;

t = 0: 1/Fs : handles.duration*(Fs-1)/Fs;

fa1 = 10^(handles.level1/20);%calculating the factor to multiply the signal by

y1 = fa1*sin(2*pi*handles.freq1*t + handles.rad1*pi)';% actual signal

sound(y1,Fs)

Thank you.

• It looks like you might have a bunch of code buried in your GUI in the form of callback functions that you can't see. – Scott Seidman Jul 29 '13 at 20:18
• I double checked everything; looks like they are in order and the handles corresponds to their respective values. But is it the proper way of doing it though? Should the dB recorded in the dBmeter go down by 6dB is I put -6dB as my input? – Ali P Jul 29 '13 at 20:31
• The most direct way to understand what is being displayed in the dBmeter is to look at the callback function for that part of the gui. If there's a property inspector for the GUI, you should be able to click around and see it. – Scott Seidman Jul 29 '13 at 21:50