Sampling resolution and upsampling demonstrated
Updated: May 10 2010.
Copyright (C) 2010 Jussi Laako. All rights reserved.
Since sampling resolutions and over-/up-sampling is hard to
demonstrate over web, it is better explained using equivalent
image processing technologies. These are very closely related
to audio processing equivalents.
As a reminder, oversampling is mathematically equal to
upsampling, but typically means more constrained variant.
192/24 hires
As a first example we take hires version of the sample, this
is traditionally what is used in studios and sometimes available
as FLAC download. This is equivalent of 192/24 audio file.
44.1/16 CD
This is how the reduced resolution on a CD looks like. This is
equivalent of 44.1/16 audio file, before D/A conversion.
Filterless NOS
Now as a comparison, let's take a very minimalistic D/A conversion
without oversampling or filtering. Some people prefer these
"filterless NOS" DACs. Some artefacts can be clearly seen due to
lack of needed sharp filtering.
NOS DAC with filtering
For NOS dac with steep enough filter the result would be like this.
4x oversampling, poor filtering
A traditional old school oversampling without heavy filtering yields
following type of result. This is with 4x oversampling. Note
that it is almost invisble that the dot patterns cosists of dots of
different sizes. All dots look to be the same size. Straight
lines and curves are rough and blocky with steps, completely unlike
the original.
4x oversampling with filtering
Typical affordable proper oversampling and filtering
results in fairly good results. Not very good resolution, but
otherwise correct.
Audiophile upsampling
Typical audiophile upsampling produces slightly constrained
results, but with quite good resolution.
Highend upsampling
At last, cost-no-object high-end upsampling. All the false
steps/blocks from straight lines is gone. Smooth curves on the
logo, just like in the original. No inconsistency in the dot
pattern of the logo's lower edge or red area.