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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: No brickwall filter then? posted by Slider on February 12, 2009 at 12:11:50:
The idea behind digital playback is that if you sample a *low-pass filtered* signal, then that signal can be reconstructed *exactly*. The low-pass filter on the record side is called and "anti-alias" filter.
To do this means that the playback system *also* has to have a low-pass filter. This filter is called a "reconstruction" filter. If everything is done right, then the playback signal will *exactly* duplicate the original *low-pass* filtered signal.
So there are a couple of gremlins hiding here.
The first is that adding a low-pass filter to an audio signal will change its sound. Period.
The lower the frequency of the filter, the more it changes the sound. That is why CD sucks compared to vinyl, which has no explicit filters in the signal path. That is also why the "high-res" formats had a chance to sound better than CD.
The second gremlin is that since CD is so restricted in how good it can ultimately sound that there are a lot of people that take liberties with the playback "reconstruction" low-pass filter.
But digital oversampling filters have NO ADVANTAGE over an analog filter except that you can make a very complex one much more inexpensively than an analog one. They are simply trading a complex digital filter for a complex analog filter.
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- No Free Lunch! - Charles Hansen 20:30:32 02/12/09 (0)
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