On 08/01/18 21:59, Müller, Marcus (CEL) wrote: > please don't reply to existing emails on the Mailing List to start a > new discussion thread
Sorry about that. > Anyway: If I remember correctly, they work pretty OK – but it's hard to > mimic analog filters in digital domain, so OK might be different for > people that care more about the actual acoustic properties of the > transmission than me! Fair enough. I've just started playing with grc and did the usual FM broadcast RX thing as my Hello World - and, as a former broadcast engineer with pretty good ears - I immediately noticed that there was far too much 'top' in the the audio. I have been using the FM de-emphasis block that is shipped in the Ubuntu gnuradio 3.7.9 package - I have added any others yet. > So, I'm pretty sure you're not being thick – it's pretty possible that > GNU Radio contains a mediocre implementation. Have you seen the source > code? If you want to, we can guide you through that, and if you have > recommendations, we'll be happy to cooperate with you to implement a > better de/emph. I haven't seen the source code and wouldn't be able to do anything with it if I had. I'm an analog guy and have quite enough trouble just pointing and clicking in grc. I can't code and the maths required to calculate filter coefficients would make my head explode. That's why I'm using grc in the first place! If the block shipped with vanilla gnuradio isn't doing its job, then surely it would be best to fix that bug. When working correctly, the amplitude/frequency response should be within, ideally, 0.1 dB of the values shown. I've shown values for both 75 and 50 microsecond time constants. Freq (Hz) Gain dB (75us) Gain dB (50us) 30 0.00 0.00 300 -0.09 -0.04 500 -0.23 -0.11 1000 -0.87 -0.41 3000 -4.77 -2.76 5000 -8.16 -5.40 8000 -11.82 -8.64 10000 -13.65 -10.36 12500 -15.52 -12.15 15000 -17.07 -13.65 For pre-emphasis, obviously the gains should be positive. This .grc demonstrates the problem - the amplitude/frequency response is essentially flat: http://www.lamont.me.uk/misc/deemph_test.grc -- Richard Lamont <[email protected]> _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
