Message: 39 > Date: Sat, 20 May 2006 16:09:52 -0000 > From: "Peter Martinez" <[EMAIL PROTECTED]> > Subject: Re: [Flexradio] 16 versus 24 bit audio > To: "Flex Reflector" <FlexRadio@flex-radio.biz> > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; format=flowed; charset="iso-8859-1"; > reply-type=response > > >From G3PLX: > > Sami is right. You CAN recover a signal from noise by narrowing the > bandwidth, so if my signal was level with the noise in 24kHz bandwidth, I > could filter it to a narrower bandwidth (in software) and improve it's > SNR.
I've been wondering about this lately; Isn't this getting close to what the definition of "process gain" is? Incidentally, Analog Devices has some excellent white papers that go into the details of the tradeoffs between sensitivity, dynamic range, resolution, etc. Definitely recommended reading. But that's true regardless of the number of bits in the raw data. So long as > we have at least half an lsb of additive noise to dither away the > quantisation problem, we can always gain SNR by reducing the downstream > software bandwidth. Any more added noise at the front end than this only > makes things - well - er - noisier. The noise power calculation I did > earlier shows that there is ALREADY about the right amount of noise > inherent > in the physics to get the dither optimum for a 24-bit ADC at 0dBm. If > there > are cards with more noise than this, it's probably because the designer > couldn't get it any lower for the price, not because he chose to add more > noise for some subtle reason. > > To take Jim's points, I have only so far measured the rms noise with no > input, and not yet looked to see if there are any clues in it's spectrum - > these things would take a lot more time. Clock jitter wouldn't explain > what > I see (an output with no input) although it would certainly cause noise in > the presence of a large pure tone. I haven't tried that yet either. It would be interesting to see the spectral characteristics of the noise. Let me close this topic before Phil accuses me of cruelty to dead horses. > Before I aquired a 24-bit card, I honestly believed that 24-bit cards > would > be 8 bits better than 16 bit cards. When I did get one recently, I was > surprised to find this wasn't the case. Jim is right. 24 bit cards may > only > be slightly better than 16-bit cards. I have learned something this week. > Seems to me that the marketing folks take the number of bits in the ADC and run with it. A 16 bit card is only 14 bits, and a 24 bit card is only 18 bits, so the 24 bit card is 4 bits better than the 16 bit card. Cheers, -- Larry Gadallah, VE6VQ/W7 lgadallah AT gmail DOT com -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20060520/eadbfa34/attachment.html _______________________________________________ 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
