On 28/05/2012 20:54, Gullik Webjörn wrote: > Hi folks, > > After experimenting with codec2 / fdmdv I realised that typical PC > sound hardware is not FUN. I had a hard time finding a suitable > soundcard / microphone combination that would yield a reasonable > audio input for experimentation. I found that sampling the mic at 48ks > and then downsampling with sox to 8ks yielded a much improved result. > With this procedure I managed to produce something that after passing > through the c2enc-mod-demod-c2dec chain was usable. > > (those of you with better audio h/w might disagree :-) >
I think we discussed some time back on this list that if you have an AC97 codec then you *really* need to use only 48Khz. The AC97 and certain other cheaper sound cards over the last few years are basically locked to 48Khz and won't work at any other rate - however, they contain (really bad) resamplers to create the appearance that they support other sample rates If you just look at the waveform of something played on an AC97 at 48Khz and something else (say 44Khz) you will see all kinds of aliasing and other digital garbage on the output - I believe it's the same or worse if you try and record Basically it's probably not a mathematical discovery you have made, so much as many built-in sound cards simply perform extremely poorly at anything other than 48Khz. Clearly some moderate headroom on the input is desirable, but I doubt you need all that much headroom. Note the new Intel HD codec is pretty sparkly and so probably all newer machines won't have this issue Good luck Ed W ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
