Over Sampling vs Non Over Sampling DAC w/computer as source - Page 2

hi dyl1dyl,

 

thanks for your reply, its true what you're saying but I'm trying to work out what the difference is between UPsampling and OVERsampling or are they different terms for the same thing?

 

cheers,

matt.

Edited by pepsi123 - 9/16/11 at 11:49am

It depends on the DAC, sometimes theyre just buzzwords.

Technically, oversampling is increasing the sample rate by an integer multiple, for example converting 44.1kS/s to 88.2kS/s or 176.4kS/s. Upsampling is increasing the sample rate by a non-integer multiple, for example converting 44.1kS/s to 96kS/s or 192kS/s.

In practice there are advantages and disadvantages to upsampling, oversampling and non-oversampling. It's a balance of trade-offs. Non-Oversampling Dacs (NOS DACs) are usually filterless. This makes them very inaccurate compared to upsampling or oversampling DACs. However, some people seem to like (prefer) the distortion produced by filterless NOS DACs.

G

 

Yup, all NOS DACs do is add lots of distortion in an incredibly expensive and impossible to rectify way. They are inferior to their oversampling brethren in every way (First person to say something about square waves in an attempt to counter this gets a shoe lobbed at them).

Get a competently designed DAC.
 

 

PC as a source offers resampling algorithms superior to many low-mid class DACs, a NOS DAC that accepts hi-res formats can benefit from this. PC as transports work on the same basis the CDPs do (output bits with proper timing) but it takes good drivers or a dedicated PC to achieve comparable results.

I broadly agree with this statement. Without a reconstruction filter a NOS DAC does not conform to the requirements of Nyquist/Shannon, resulting in alias images. Resampling to higher sample rates pushes the Nyquist Point higher in frequency and more of the alias images will occur outside of the hearing spectrum. There is still the problem of inter-modulation distortion with the alias images causing artefacts in the hearing spectrum but this is likely to be less noticeable than hearing the alias images directly.

In a sense though, by upsampling (or oversampling) in the PC you are defeating the basic concept of a NOS DAC in that you are now oversampling (just not in the DAC).

G