 Hello, Didier Stevens here with another video on GNU Radio Companion that you can use without any dedicated hardware like an SDR. In previous videos we used different sources like a sine wave, a noise source. Here we are going to use a source that reads a WAV file and uses that audio that you can then further process. So you need a WAV file, a source and that's something you have to find here in the modules. Now with CTRL F you can search here. So CTRL F and let me type WAV like this. Okay, so in audio I have a WAV file source. So I select this. I'm going to do this without repetition so that the WAV file only plays once. And then here in test user documents I can find here a recording like this. Now this is a WAV file that was recorded at 44.1 kW. So the typical frequency for WAV files and that's also the frequency of a compact disc audio if you're still familiar with that. So I need to change my sample rate here to 44100. And then in my audio I need an audio sync for the speaker like this. I can connect this, save it. So WAV and then I can play it. This is WAV recording. So that was a recording that I just made here and I'm playing it back using here GNU radio companion. Now if I change the sample rate here, if I put it at 48000 like I did with the other examples, then I will actually use a higher sample rate than the sample rate with which the WAV file was recorded. And let me play this back. This is WAV recording. So now you hear my voice with a higher pitch and would I have used 32000? So a sample rate lower than the actual sample rate. This is WAV recording. So now you hear my voice much lower. So let's come back to the actual sample rate 44100. Okay. And now I'm going to put in a filter. Remember we talked about filters and I use the bandpass filter here. Like this. So I'm going to insert this here. So float, float. And then again I'm going to use the frequencies of the telephony system. So 300 to 3000 hertz. Transition of 10. And then I can play back my WAV file. And now you will hear that it sounds like coming out of a telephone handset. This is WAV recording. And this here is just actually the same as in the previous video that I made, the previous examples. But instead of using a noise source here, now we are using a WAV file. And then you can process any sound that you wish as long as you can create a WAV file for it. And just one last thing that I'm going to show you here is to make some echo. So let me remove this. So an echo is actually a repetition of the signal but with the delay. So you have in a new radio companion a module to introduce delays here. Let me use that module. And then what I want to do is combine the WAV file without any delay together with the delayed WAV file. So for that I need to add. So that's something we also did here, mat operators. And we are going to do an addition like this. And everything needs to be in float like this. And the delay here, if you look in the documentation, the delay is specified in the number of samples. So since my sample rate here is 44.1, I'm going to use that as a delay. I'm going to delay this for 44100 samples. So that's one second. And instead of typing 44100, I can say sample rate like this. And you see here appearing 44.1. So my original audio is going from the WAV to the addition to the audio sync. And then I'm going to delay this same audio and put it here in the addition to the audio sync. And now we can play this and you will hear an echo of one second. This is WAV recording. As you can see here you heard the recording twice. But it's not a really natural echo. So I'm going to speed this up a bit and I'm going to do this one tenth of a second. So device the sample rate by 10. Here you can actually input Python expressions. So this is a variable divided by 10. So let's play this and you will hear that this sounds more like a natural echo. This is WAV recording. And now what also typically happens with echoes like that is that the second and sometimes a third and you can have more than one echo. So that the second signal is a bit fainter than the original one. And that's also something you can do by multiplying here with a constant. So let me add this and so float float. And I'm going to divide this by two. So I'm going to multiply this with 0.5. And so my signal here will be half like this. And then I can again listen to the echo. This is WAV recording. So here you had some simple examples to show you how you can use GNU radio companion here with WAV files. And then do some simple tricks like filtering to have a certain audio effect or all echoes like here I did with the delay.