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Re: [Discuss-gnuradio] audio sink issue

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] audio sink issue
Date: Mon, 15 Dec 2014 13:57:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

Hello Sreena,

the frequency translating FIR translates and then filters, ie. it moves your baseband signal to -19kHz and then filters a 1kHz band around 0Hz -- thus cutting away all your signal.

By the way: I assume you want to produce sounds at 19kHz with your built-in sound card: you won't hear much [1] unless you're very young, and your sound card has wide filters -- most cost-conscious soundcards will simply have only exactly one very simple analog filter with a cutoff frequency around 20kHz, and don't pay much attention to a narrow transition width, since humans won't easily notice attenuation in frequencies they can barely perceive anymore, and most speakers won't be linear at high frequencies, either.



On 12/15/2014 01:08 PM, sreena p h wrote:

I am trying to implement the following acoustic communication transmitter with PC

File Source --> Packet encoder --> gmsk mod --> Rational resampler     --> Frequency Xlating FIR filter  --> comp to real --> audio sink

Pc has inbuilt sound card. packet encoder is taking 8 samples per symbol, Resampler interpolates samples by 500, FIR filter is set at 19k carrier frequency and 1K bandwidth. 

The problem is that I wont get any sort of output at the audio sink. I added an GUI FFT sink at the end of FIR filter, it also showed now output. Please tell what's gone wrong. I am using gnuradio 3.7.4 version.

Thanks in advance 

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