Sugestions or Comments about my Sound Tutorial

[rm_03]

I really like the resampling function, I tried that before but failed on downsampling, although I havn't tested yours yet.
It looks like you're using linear interpolation, cubic or Hermite interpolation should increase the quality.
(http://astronomy.swin.edu.au/~pbourk...ion/index.html)
I've also heard you should do low pass filtering to remove frequencies above the new Nyquist frequency when downsampling, but never dealed with it.

Anyway, I've just ported a Goertzel algorithm (Fourier transformation, but only for 1 frequency)
for tone detection to VB,
maybe you can use it for your tone detection topic:

Function Goertzel( _
    sngData() As Single, _
    ByVal N As Long, _
    ByVal freq As Single, _
    ByVal sampr As Long _
) As Single

    Dim Skn     As Single
    Dim Skn1    As Single
    Dim Skn2    As Single
    Dim c       As Single
    Dim c2      As Single
    Dim i       As Long

    c = 2 * PI * freq / sampr
    c2 = Cos(c)

    For i = 0 To N - 1
        Skn2 = Skn1
        Skn1 = Skn
        Skn = 2 * c2 * Skn1 - Skn2 + sngData(i)
    Next

    Goertzel = Skn - Exp(-c) * Skn1
End Function

Function power(ByVal value As Single) As Single
    power = 20 * Log(Abs(value)) / Log(10)
End Function

Usage: (returns dB of 8000 Hz in the signal at 44100 samples/s)

dB = power(Goertzel(sngSignal, UBound(sngSignal) + 1, 8000, 44100))

I also did some testing with DTMF tone detection,
it can detect a generated tone in 0.01 seconds in the IDE
(compiled with optimizations 0.001 s), which is pretty fast on a P3 550 Mhz, I think.

[CVMichael]

It looks like you're using linear interpolation, cubic or Hermite interpolation should increase the quality.
(http://astronomy.swin.edu.au/~pbourk...ion/index.html)
I've also heard you should do low pass filtering to remove frequencies above the new Nyquist frequency when downsampling, but never dealed with it.

Thanks for the link.

I implemented the Cubic and Hermite interpolation from the link you gave me, but I don't see significant diferences between linear and the other 2.

Hermite looks best compared to the original.

I will make another test program that will convert wave files and save them into new ones, so that I can hear the diference.

I attached a test project, please take a look at it, and tell me what you think ?

I did not have time to take a look at the rest of the code you gave me. I'm very busy lately.

[rm_03]

I implemented the Cubic and Hermite interpolation from the link you gave me, but I don't see significant diferences between linear and the other 2.

Take a look at this:
http://musicdsp.org/files/other001.gif

I attached a test project, please take a look at it, and tell me what you think ?

Very nice stuff, hopefully this has some real time capabilities

[CVMichael]

Take a look at this:
http://musicdsp.org/files/other001.gif

I have no clue what i'm seeing in that gif...

Very nice stuff, hopefully this has some real time capabilities

Well, if in VB is not fast enough, it can always be converted to a C++ DLL, and used in VB like API... that will be fast for sure

[rm_03]

I have no clue what i'm seeing in that gif...

X is frequency, Y is dB at that freq.
The blue line is perfect interpolation, how it should look like.
The green line is "no interpolation", and turns into a lot of audible distortion.
The pink line is linear interpolation, which already has a better quality.
The black line is cubic interpolation, and has the lowest distortion.

A perfect interpolation would be using sinc functions, I heard.

[CVMichael]

Usage: (returns dB of 8000 Hz in the signal at 44100 samples/s)

dB = power(Goertzel(sngSignal, UBound(sngSignal) + 1, 8000, 44100))

I also did some testing with DTMF tone detection,
it can detect a generated tone in 0.01 seconds in the IDE
(compiled with optimizations 0.001 s), which is pretty fast on a P3 550 Mhz, I think.

I finally had time to try it.

I'm speechless, very nice !

It's soo precise !
I tried with a dual tone with frequencies (tones from the phone): 770 Hz and 1209 Hz (wich coresponds to #4 on the phone)

I made a short program that tests with all the frequencies from the phone, and I got this:
First number is the frequency and in brackets is the dB
Test1:
350(075.87) 440(060.86) 480(046.48) 620(076.66) 697(077.03) 770(171.13) 852(068.98) 941(042.27) 1209(171.14) 1336(067.06) 1477(062.78)
Test2:
350(075.87) 440(060.86) 480(046.48) 620(076.66) 697(077.03) 771(111.53) 852(068.98) 941(042.27) 1209(171.14) 1336(067.06) 1477(062.78)

If you notice In the first test for the frequency 770 the volume is 171, and for frequency 1209 is the same.
The second test, I changed it to test for 771 Hz instead of 770 Hz, and the result is 111 dB

The diference in frequency is only 1 Hz, but a very big diference in dB (wich is very good)

Pretty fast too...

Though I made the test with digitaly created wave files (wich have perfect quality), not actual tone from the phone. I want to test for that too, but I don't have time right now.