Product Review
 

ONIX CD-3 CD Player

Part IV

May, 2007

John E. Johnson, Jr.

 

At 20 kHz, the effects of upsampling on THD+N were even more pronounced. Notice that the amplitude resolution of the 20 kHz peak increased by 10 dB. The base of the peak was at - 110 dB with no upsampling, and at - 120 dB with upsampling turned on. In all tests, THD+N remained lower than 0.003%.

The measured frequency response was 20 Hz - 20 kHz ± 0.05 dB. That is superb!

When CD players were originally marketed, the digital sampling frequency was 44.1 kHz and the word length was 16 bits. The Digital-to-Analog decoders (DACs) were only able to operate within those limitations.

However, with improvements in DACs, higher frequencies were soon obtainable. Engineers realized that quantization noise, which is the result of errors produced by the fact that analog voltage values in the music have to be assigned the nearest 16 bit digital number to that value, rather than always being the exact value, could be reduced by oversampling the 44.1 kHz sampling to multiples of that, during the conversion to analog signals. This noise is the difference between the analog signal value and the digital number that represents it. The difference is small, and therefore, it is very high frequency. Quantization noise, even though it is not in the audible band, causes aliasing, which has an effect on frequencies in the audible band, resulting in more harmonic distortion.

At first, oversampling was 4X (176.4 kHz), and then later, 8X (352.8 kHz).

The higher sampling frequency with oversampling pushes the quantization noise so far away from the audible band, filters in the output stage have a much easier task in removing the noise.

Upsampling is basically the same process, but is strictly in the digital domain, and was created to let DACs that are used in the new high resolution music formats, such as DVD-A and SACD, easily decode CD music. The reason this requires its own special procedure is that high resolution music formats are not integer multiples of 44.1 kHz. For example, DVD-A uses 96 kHz and 24 bit word lengths (a 2X integer multiple of 44.1 kHz would have been 88.2 kHz). Likewise, SACD uses a number that is not an integer multiple of 44.1 kHz.

However, the results are the same: reduction of quantization noise in the analog signals sent from the CD player, to the preamplifier.

Upsampling is a newer technology, and sometimes it is used in a CD player to reduce quantization noise, even though the player only plays standard CDs rather than high resolution music formats. Such is the case for the ONIX CD-3.

Conclusions

If you are in the market for a standard CD player, the ONIX CD-3 is a must for your consideration. At $999, it is one of the best values in audio for 2007.

 

- John E. Johnson, Jr. -

© Copyright 2007 Secrets of Home Theater & High Fidelity

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