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RE: Upsampling question

Posted by Todd Krieger (A) on November 11, 2007 at 01:53:14

In Reply to: Upsampling question posted by greg7 on November 10, 2007 at 15:29:43:

"Sorry for the recent barrage of questions but here's another: when is upsampling subjectively 'good' and 'bad'?"

Upsampling's or oversampling's intended purpose was to digitally filter out the ultrasonic frequencies above 22 kHz. And unless the device is explicitly stated as non-oversampling (or is the initial Sony design), they all upsample/oversample.

Although there is no official distinction between upsampling and oversampling, the most-common is oversampling being "synchronous," and upsampling being "asynchronous." (Synchronous is often stated as 4x/8x/16x etc. oversampling. Which was predominant during the 1990s.) I personally think asynchronous upsampling is very fatiguing to listen to. It injects a narrow band of HF noise that to me sounds "detailed" initially, but over time, I realize that it's actually noise riding on the music. And I ultimately become fixated on that band of noise. (See link in regard to how this noise occurs.)

Conversion from 16/44 to 24/96 in real time was *not* the original intention of sample rate converters. It was to enable music to be transferred from one medium to another. Like from CD to DVD. These converters only became popular in their current form because of marketing and a couple rave reviews of the dCS Purcell upsampler. (I saw the "bogus" in the product from the very beginning.) Then it was all downhill from that point.

"I've been under the impression that all upsampling is 'bad' (un-musical) in general?"

Not only do I think it's bad, I think it's a technological fraud..... (As a real-time processor.) There is nothing, technically speaking, where such process would suggest improved signal fidelity. The review of the dCS Purcell was what made "24/96" or "24/192" upsampling the hottest new product in audio.

"Two players I'm considering use 192 kHz and 96 kHz, respectively. Both use current generation 24 bit chipsets. Are both at least synchronous? And is 'less' better (i.e., lower upsampling frequency)?"

I've fallen into this trap personally. The chips are often *capable* of playing up to 96 or 192 kHz, but unless a sample-rate converter (SRC) chip is part of the chipset, it's *not* asynchronous. But I do think these newer chips sound worse than the 20-bit chips used during the 1990s.

All else being equal, I also prefer 24/96 over 24/192. But that's not an endorsement of 24/96.

"Are there any general rules of thumb here? I realize upsampling is only one of a multitude of variables lending to sound quality but I'm curious to understand."

My only suggestion is to gather the information, ask questions regarding the validity of marketing claims, and audition as many different players as you can. (You may end up liking asynchronous upsampling.) But I will add that you should extend your listening sessions to at least an hour, to get the big picture. Since a lot of the ills of digital playback don't become apparent in brief listening.

• http://db.audioasylum.com/cgi/m.mpl?forum=digital&n=122532   (Open in New Window)

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