Ok,
I have a question will I really notice that much of a difference is I choose to buy an upsampling CD player as opposed to a CD player with high end dual DAC's?
I mean upsampling versus regular high end... is it worth $400... and when I listen to the test... what should I listen for?
Let me know.
Most modern CD and DVD players use a digital-to-analogue converter which converts the original signal to one with a higher sampling rate than the original sample rate. This is done via interpolation of sample values. This means that an upsampling DAC is similar to an ordinary DAC which interpolates.
If you were to compare a DAC to another upsampling DAC, you would need to do so with both units level-matched (to 0.1 dB, I think), and the comparison would need to be made under double-blind conditions. Unless the comparison is made in these conditions, assertions of differences between the units could be imaginary.
Modern DACs typically offer superb performance:
'High quality CD players often deliver frequency response flat within 0.1 dB from 20 Hz to 20 kHz. THD+N below –90 dB is available from CD players in almost any price class, and very good CD players may have distortion below –95 or –96 dB. Linearity error within 1 dB down through the -100 dB signal level is possible with the best CD players.' [1]
With some specialised signals, e.g., sinusoids, you may be able to detect differences between CD players. This may be due to differences between the players in levels of background noise or low-level linearity (see [2] for a discussion on the audibility of background noise). In ordinary listening, the signals which generate these errors can actually serve to audibly 'mask' the error itself.
One argument I've heard put forward for upsampling is potentially improved jitter performance [3]:
'Data-to-System synchronization allows any incoming audio stream to be resynchronized and retimed to a local high quality clock. By using a stable clock reference, the negative effects of inter-component jitter can be minimized. When converting the digital audio to an analog signal through high performance D/A converters, this reduction in jitter has enormous benefits in the level of detail and clarity in the reconstructed analog sound. Combining this process with a virtual time domain model that uses an advanced cubic interpolation algorithm to resample the incoming audio data, timing errors in this signal can be compensated for at amazing levels of accuracy. The end result is tighter, more focused bass, increased stereo imaging, focus and separation for all musical instruments and voices.'
Although this argues for potential improvements in sound quality, there is no reference to any high-quality perceptual research to back this up. Based on what I've read on jitter audibility, I am doubtful that existing CD/DVD players have indequate jitter performance [4,5]. Poorly designed digital audio equipment, e.g., some early computer sound cards, may have jitter-induced errors high enough to be audible in ordinary listening [6].
[1] Metzler, B. (2005). "The Audio Measurement Handbook". Second edition for PDF. Page 137. Audio Precision, USA.
http://ap.com/library/books.htm
[2] Stuart, J. (n.d.). "Coding High Quality Digital Audio". Meridian Audio Ltd, UK.
http://www.meridian-audio.com/ara/coding2.pdf
[3] Adams, B. (2005). 'Can You Change the Past?'. Analog Devices, Inc.
http://www.analog.com/communities/audio/BobsColumn/column0806.html
[4] Dunn, J. (2003). "Measurement Techniques for Digital Audio". Page 34. Audio Precision Application Note #5, Audio Precision, Inc. USA.
http://ap.com/library/technotes.htm
[5] Ashihara, K. et al (2005). "Detection threshold for distortions due to jitter on digital audio", Acoustical Science and Technology, Vol. 26 (2005) , No. 1 pp.50-54.
http://www.jstage.jst.go.jp/article/ast/26/1/26_50/_article
[6] Krueger, A. ' PCAVTech Sound Card Technical Benchmarks Test Summary'.
http://www.pcavtech.com/soundcards/summary/index.htm