13-11-2023, 10:12 AM
(This post was last modified: 13-11-2023, 10:26 AM by Mike Watterson.)
Yes, if 44.1 kHz is good enough, so is 44 kHz, but 44,000 / 30 = 1466.66666667 (but PAL 25 fps works) and 48 kHz is better. Of course the running time of CD is then 44.1/48 = 0.92 approx. Obviously, forgetting about PCM to video adaptors, you want as low a sampling rate to have more content on the CD (mysteriously they'd decided on 8 cm diameter before they started), and as much higher as possible than twice highest audio frequency to have a simpler, cheaper anti-aliasing filter, because in the 1970s you were not going to sample at 180 -200 kHz at 16 bits and digitally filter like is done now.
As an aside, ADI now has ADCs that have 8 ADCs with a psuedo random sampling that you pretend is one faster ADC. The guy working on it says, "No, we are not using the ADC as a mixer for the 5 GHz receiver, it's really sampling at over 10.2 GHZ. Then there are two stages of DSP doing filtering and decimation to have two streams of 100 MHz sampled data."
Because due to power consumption being almost a square of sample rate, you "down convert" as soon as possible. In analogue radio days 1st IF was high for image rejection (6 MHz to 200 MHz) and 2nd was low (100 kHz to 1.6 MHz) to set final bandwidth. I pointed out to him the curious similarity that now even though direct SDR sampling for 5 GHz receivers exists, that they are back to "dual conversion", but for power consumption efficiency rather than image rejection and bandwidth. He was fascinated that Icom has "pure" SDR for HF but that my Yaesu was hybrid so as to have more ADC resolution and thus better dynamic range. He immediately wondered why the spectrum display ( up to 1 MHz wide and more "pure" SDR) couldn't show an alternate band. I said I'd have to study the HW (I have schematic) to see if a HW limitation or indeed possible in "firmware".
As an aside, ADI now has ADCs that have 8 ADCs with a psuedo random sampling that you pretend is one faster ADC. The guy working on it says, "No, we are not using the ADC as a mixer for the 5 GHz receiver, it's really sampling at over 10.2 GHZ. Then there are two stages of DSP doing filtering and decimation to have two streams of 100 MHz sampled data."
Because due to power consumption being almost a square of sample rate, you "down convert" as soon as possible. In analogue radio days 1st IF was high for image rejection (6 MHz to 200 MHz) and 2nd was low (100 kHz to 1.6 MHz) to set final bandwidth. I pointed out to him the curious similarity that now even though direct SDR sampling for 5 GHz receivers exists, that they are back to "dual conversion", but for power consumption efficiency rather than image rejection and bandwidth. He was fascinated that Icom has "pure" SDR for HF but that my Yaesu was hybrid so as to have more ADC resolution and thus better dynamic range. He immediately wondered why the spectrum display ( up to 1 MHz wide and more "pure" SDR) couldn't show an alternate band. I said I'd have to study the HW (I have schematic) to see if a HW limitation or indeed possible in "firmware".
