AT commands for dialing and receiving calls by use of usb modem in laptop on landline telephone cable

Question

I am doing a project that is for making calls by using usb modem, i have done with call making and sending an audio file to the receiver end but when receiver receive the call the noice begin coming from there instead of that audio file.how to change that noice into hear able voice so the receiver can hear it properly. i am following this link. https://www.daniweb.com/programming/software-development/code/313281/playing-wav-over-modem

here i found that i have to go and change the speech Rate variable, which is part of the TAPI SDK. but i don't know where is tapi sdk and how to change is made up. and secondly if someone help me to make enable calls voice in calls that i can make from usb modem to mobile phone. here is my code that i am using to make calls with no voice and sending audio file that converts into a noice.

serialPort1 = new System.IO.Ports.SerialPort("Com3", 115200, System.IO.Ports.Parity.None, 8, StopBits.One);
serialPort1.DtrEnable = true;
serialPort1.Open();
//Switch to Voice Mode
serialPort1.Write("AT+FCLASS=8" + System.Convert.ToChar(13).ToString());
//Call Number
serialPort1.Write("AT+CLIP=1" + System.Convert.ToChar(13).ToString());
serialPort1.Write("ATDT+ HERE I PUT MY PHONE NUMBER" + System.Convert.ToChar(13).ToString());
System.Threading.Thread.Sleep(17000);

//Enter Voice-Transmission Mode
serialPort1.PinChanged += new SerialPinChangedEventHandler(serialPort1_PinChanged);
serialPort1.Write("AT+VTX" + System.Convert.ToChar(13).ToString());

bool MSwitch = false;
byte[] buffer = new byte[500000];
FileStream strm = new FileStream(@"D:\m.wav", System.IO.FileMode.Open);
MemoryStream ms = new MemoryStream();
int count = ms.Read(buffer, 44, buffer.Length - 44);
BinaryReader rdr = new BinaryReader(strm);
while (!MSwitch)
{
    byte[] bt = new byte[1024];
    bt = rdr.ReadBytes(1024);
    if (bt.Length == 0)
    {
        MSwitch = true;
        break;
    }
    serialPort1.Write(bt, 0, bt.Length);
}
strm.Close();
strm.Dispose();
serialPort1.Write("ATH" + System.Convert.ToChar(13).ToString());
serialPort1.Close();

Answer 1

Make sure that the wav file has the same settings as the selected option in the modem. To check the supported options in the modem execute this command:

AT+VSM=?

result e.g.

0,"SIGNED PCM",8,0,8000,0,0
1,"UNSIGNED PCM",8,0,8000,0,0
129,"IMA ADPCM",4,0,8000,0,0
130,"UNSIGNED PCM",8,0,8000,0,0
131,"Mu-Law",8,0,8000,0,0
132,"A-Law",8,0,8000,0,0
133,"14 bit PCM",14,0,8000,0,0

Then you can select one of them:

AT+VSM=131,"Mu-Law",8,0,8000,0,0

8000: (sample per second). 8: (bit per sample).

Another thing as I remember, that you should execute AT+FCLASS=8 (which enables the voice mode if the modem supports the voice feature) after the calling command.