Don't forget John, that the 44kHz lobes on the crummy looking 20kHz square wave of yours are going to be filtered out before it gets to the output. Then you will have a nice clean 20kHz sine wave again.
Steve
----- Original Message ----- From: John van Ommen jvanommen@verio.net To: hanslaros@hotmail.com Cc: bass@lists.cc.utexas.edu; mad-user@lists.mars.org Sent: Thursday, February 21, 2002 2:22 AM Subject: RE: Huuuuuuuge Improvement to My Stereo
It's really hard to explain why upsampling works without resorting to graphs. Basically, audio theory says that 40,000khz is adequate to play back a 20khz sinewave. But if you think about it, a sampling rate of only 44,000 hz gives a VERY crude approximation of a sine wave. Sure, the peaks and the valleys are there, but the sine wave now looks more like a square wave than a sine wave.
With upsampling, you can interpolate that waveform to *approximate* a sine wave. Obviously, the best solution would be to do the original recording at a extremely high sampling rate.
John
P.S.
Here's my graph:
Analog 20khz sine wave : ** ** * * * * * * * * * * * * ** and here's what a 44khz DAC does to a 20khz signal:
**** **** **** **** **** **** **** **** ****
As you can see, there's little more than a passing resemblance to a sine wave at that sampling rate, the interval is too coarse.