Hi Tom, thanks for you feedback.
I didn't try your suggestion yet. But my professor help me to solve this in a different way: we put a divisor after the FFT (the divisor value is the same as the FFT size). Its related to the equations associated with the FFT and IFFT: in a real system the FFT (or the IFFT) divides the outputs by N (the FFT size), this division is required in order to the other transformation, in this case the IFFT, recover the signal with the same dB values. I think that the GNu Radios developers have not placed this division inside the FFT block because if you two of them, you will have the signal divided 2 times, and not one. abc On Tue, Oct 9, 2012 at 11:17 AM, Tom Rondeau <[email protected]> wrote: > On Mon, Oct 8, 2012 at 8:24 AM, Maicon Kist <[email protected]> wrote: > > Hi list, > > > > I'm trying to recover a sound after passing it by a FFT and a IFFT. The > > problem is that after the IFFT (to recover the original sound) and > sending > > it to the audio sink, I hear only wheezings. > > > > Attached to this email is the system that I created using the GNU Radio > > Companion tool. > > > > Do your guys have any suggestion to recover the sound ciorrectly? I think > > that maybe is something with the sample frequency. > > > > Thanks. > > > > abc > > There are two things to watch out for here. > > First, you made the classic mistake of using a throttle and a hardware > block in the same flowgraph. The audio sink you have is the block that > will do your sample rate control. You do NOT need a throttle block. > It's not even that the throttle is unnecessary, but it will screw up > your program. You have two clocks now competing for flow control. The > throttle block is just a very poor approximation of a flow control > based on the CPU and timers. > > Second, you might want to specify the device in the audio sink. By > default, it's likely that you are using the ASLA sink, which provides > no sample rate conversion. At 48 kHz, you might be ok. If you use > pulseaudio (in Ubuntu, this is available by default now), for the > 'Device name' parameter in the audio sink's options, you can use > 'pulse.' > > Recreating your graph on my machine with these two changes worked fine. > > Tom >
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