# Audio sink issue

**URL:** <https://www.ruby-forum.com/t/audio-sink-issue/233453>\
**Category:** GNU Radio\
**Created:** [December 15, 2014, 1:10pm UTC](https://www.ruby-forum.com/t/audio-sink-issue/233453 "2014-12-15T13:10:18Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [December 15, 2014, 1:10pm UTC](https://www.ruby-forum.com/t/audio-sink-issue/233453/1 "2014-12-15T13:10:18Z")

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Hi  
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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**Author:** ![sreena\_p\_h](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/47e85d/32.png) [@sreena\_p\_h](https://www.ruby-forum.com/u/sreena_p_h)\
**Post date:** [December 15, 2014, 2:07pm UTC](https://www.ruby-forum.com/t/audio-sink-issue/233453/2 "2014-12-15T14:07:31Z")

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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.

Greetings,  
Marcus

[1][Frequency Range of Human Hearing - The Physics Factbook](http://hypertextbook.com/facts/2003/ChrisDAmbrose.shtml)