On 5/20/06, Philip Covington <[EMAIL PROTECTED]> wrote: > On 5/20/06, Peter Martinez <[EMAIL PROTECTED]> wrote: > > from G3PLX: > > > > Hello Sami. Thanks for joining the discussion - I feared I was on my own for > > a while! I hope some others will contribute too, so I don't get accused of > > hogging the bandwidth (or perhaps generating too much noise!). > > > > You said: > > >If your low 8 bits are truly random with no input, that's a good > > >thing! It follows that when you inject a non-random signal, it will > > >stand out clearly from white noise. > > > > Let me be simple-minded and respond:- > > > > But if my low 8 bits are truly random and I inject an 8-bit sinewave, isn't > > it then level with the noise? If I could reduce my 8 bits of added noise to, > > say, 4 bits, wouldn't my sinewave then be 24dB above the noise? I don't see > > how adding that much noise can ever be a good thing to do. I am not trying > > to trap you, I really would like to understand what's going on here. This is > > all new stuff to me. > > > > I had a private email from a broadcast engineer who confirmed what I was > > saying about dither noise. He said they added 0.5 bits-worth of white noise > > to the analogue signal before digitisation, and subjectively that was the > > best result. > > > > But that's half a bit of dither, not 8 bits. > > > > 73 > > Peter > > Really, its like we are continuing to beat a dead horse here... a 24 > bit card is not going to give you the theoretical 24 bits of > resolution, just like a 16 bit card does not necessarily give you its > theoretical 16 bits of resolution. Now some 16 bit cards can come > close, but most 24 bit cards under $1000 are really going to give you > << 18 ENOB. Go back and do a search of the Flex Forum... there are > examples of so called 24 bit cards that are much worse than some of > the better 16 bit cards. > > When they say 16 bits or 24 bits, the manufacturers are refering to > the ADCs rated resolution stated by its manufacturer. The design of > the ADC front end, board layout, power supply filtering, etc... > determines whether the board will even come close to the ADC rated > specs (which are sometimes very optimistic in the first place). > > The Delta 44 became the recommended card for the SDR-1000 for a long > time because in its price range, its performance was good, it has two > ins and two outs, and ASIO drivers were available for it. > > Phil Harmon has just completed testing of the AKC ADC in the JANUS > ADC/DAC board. He is seeing great numbers... this is the ADC used in > one of the < $1000 cards. We are not going to see 24 bits, but it > will be much better than the Delta 44 or the Firebox. > > 73 de Phil N8VB
P.S. I was so jaded by all this ADC "bit" stuff that when discussions were going on in the old Xylo group about which ADC to use, I lobbied hard for the TI PCM4202 since it was easy to get compared to the AKM AK5394A part and I was convinced that the performance would not be all that much better. Well, I was definitely wrong about that one... this came out in testing... A few very smart individuals were suggesting all along that we look at the AKM part. I am glad that Phil VK6APH and Bill KD5TFD continued to test all possibilities... 73 de Phil N8VB _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
