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In Reply to: Re: Why would you choose to upsample to 96 instead of 88.2.... posted by Ted Smith on January 18, 2007 at 17:32:09:
I'm assuming there's a whole shed-load of (unnecessary) number-crunching/re-quantizing in converting 44.1 to 96KHZ.Every single sample re-quantized?
As I understand it, this is not the same as 'over-sampling' (it's done prior to A/D conversion and digital filtering), so surely using factors of the 'native' sample-rate has got to be the way to go?
Follow Ups:
looks like there is only one more step *division*
96 (= 320/147 x 44.1)
HowdyNope, it's more complicated:
This is Asynchronous Sample Rate Conversion (ASRC) vs. Synchronous Sample Rate Conversion.
With SSRC there is only one clock. Or to be more accurate the output clock is derived from the input clock synchronously: usually in a rational manner, i.e. twice as often as the input or 320 times for each 147 times on the input. The math to derive the output samples is fairly simple in principle, e.g. for 44.1 to 96 put in 319 zeros between each input sample, filter the stream at 22.05 and output every 147 sample. If you are careful you can save a lot of math by not calculating the samples you don't need and skip over all of the multiplies by zero...
With ASRC there are two independent clocks, the input and the output. In a theoretical sense you upsample the input to a high rate and then use the output clock to pick samples at the right time perhaps using interpolation between the samples when the clocks aren't perfectly aligned (and they will rarely be aligned.) ASRC has the advantage that the output clock can be very controlled (low jitter) and the DAC can be optimized for that rate. It has the "feature" that any input jitter is encoded in the data. The results of this can be either better or worse than SSRC depending on the input jitter and the jitter sensitivity of the DAC proper...
Wow, there is a lot that goes into this whole upsamping DAC, clocking, jitter thing....all this just to get good sound out a digital media.The more I try to tweek, wire, upsample, de-jitter, and eq the nasty digital sound out of CD's, the more frustrated I get.
BTW, I did listen the 88.2 and I noticed a greater length of decay and a slight sense of air....maybe because of my room though, that added a bit more lively sound to the music....which wasnt good in my already lively room.
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