[linux-dvb] How does bad reception influence quality of macroblocks?

Richard Scobie r.scobie at clear.net.nz
Fri Feb 16 07:54:45 CET 2007



lynx.abraxas at freenet.de wrote:

> This  is  very valuable to know. Sadly I couldn't find any info on this in the
> net.
> What would You recon is ment with "signal strength" and  "signal  quality"  in
> the  M$  windows  dvb-t  programme?  Would  it  be  SIG and SNR as reportet by
> dvbsnoop or tzap?  What  do  the  other values discribe? SNR is never changing 
> although it is reported. Here is  some  output  of usbsnoop and tzap:
> 
> tzap ard
> using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
> reading channels from file '/home/lynx/.tzap/channels.conf'
> tuning to 191500000 Hz
> video pid 0x0201, audio pid 0x0202
> status 03 | signal 8675 | snr 0000 | ber 001fffff | unc 00000000 |
> status 1f | signal 8435 | snr 0000 | ber 00000000 | unc 00000013 | FE_HAS_LOCK
> status 1f | signal 8455 | snr 0000 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
> status 1f | signal 844e | snr 0000 | ber 00000000 | unc 00000000 | FE_HAS_LOCK

The crucial ones here are ber and unc.

Ideally both should be zero. BER is a measure of bit errors in the 
stream and up to a certain point, these errors are fully corrected with 
the original data able to be recovered by using the error correction 
code which is part of the encoding.

Once the number of errors exceeds the error correction capability, the 
picture/sound starts to show visible/audible artifacting and this will 
show up in the unc - uncorrected errors column.

I am a little puzzled as to why the second entry in your example is 
showing uncorrected errors and yet has a ber of 0.

The ber numbers can be quite useful for fine tuning your dish alignment, 
particularly LNB skew.

Regards,

Richard



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