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SONIC AD2K+
Some Notes on Word-Length Reduction Systems:
There are a variety of Word-Length Reduction systems on the market. Often, the terms "dithering" or "redithering" are used to describe these systems. Word-Length Reduction actually refers to any process that takes a higher word length and reduces it to a lower word length. Typical applications include accomodating a lower resolution recording device or transmission systems. At this time, the most prevalant word-length reduction systems take 24-bit samples and process them to 16-bit for DAT or CD compatibility. All word-length reduction processes degrade the audio uality to some extent. The best systems can achieve apparent 20-bit performance in a 16-bit channel.
Since many users record a wide variety of content in various settings and with different equipment it is important to have more than one WLR system available.
The SONIC AD2K+ from Sonic Sense and Benchmark Media features three types of Word Length Reduction techniques: NN™, NS™, and TPDF (Triangular Probability Distribution Function) dither.
Benchmark NN™ and Apogee UV™ are examples of Near Nyquist word length reduction systems. By definition, the Nyquist frequency is 1/2 the sample frequency or 22.05KHz at 44.1 kHz. Near Nyquist systems place most of the dither noise energy between 18 kHz and 22 kHz while maintaining a nearly white noise-spectrum below 16 kHz.
In contrast, the Benchmark NS™ system shapes the lower frequency noise for minimal audibility. Unlike NN™, NS™ does not have a white noise-spectrum below 16KHz. However, it is very important to understand that the NS™, NN™ and UV22™ systems all have very similar spectral characteristics between 18 kHz and 22 kHz. All three systems will have very similar performance characteristics above 18 kHz. All of the significant performance differences lie below 18 kHz.
The Benchmark NS™ system differs from the UV22™ and NN™ systems in that it provides increased resolution in the two most critical bands. These critical bands lie between 2 kHz and 6 kHz, and between 11 kHz and 14 kHz. NS3™ exceeds 20-bit performance at 4 kHz, and exceeds 18-bit performance at 12 kHz. In contrast, Near Nyquist systems are limited to a resolution of 17 to 18-bits at all frequencies below 16 kHz. The above discussion implies that the Benchmark NS™ system will always provide better results than a Near Nyquist system. However, it is important to note that the NN™ system outperforms the NS™ system in the much less critical 8 kHz to 10 kHz band. The advantages of the NS™ system come at the expense of a small loss of resolution between 8 kHz and 10 kHz. In most situations this is a good trade off, and consequently, NS™ usually will produce the best results.
However, there are at least two situations where the Benchmark NN™ system can outperform the Benchmark NS™ system:
1) In a noisy recording environment the performance benefits of NS3™ may be lost in the due to the masking effects of high noise levels in the room. Under such conditions, the NN™ system may provide equal performance at most frequencies, and slightly better performance (slightly more resolution) in the less critical 8 kHz to 10 kHz band.
2) If anticipated playback levels will be high enough for the NN™ and NS™ noise floors to be heard, the NN™ noise floor will sound more natural. At 16-bits, NS3™ remains inaudible as long as the playback system is adjusted for a peak sound pressure level of less than 107 dB at 0 dBFS (Above rock concert volume). NS3tm will still out perform NN3™ at peak playback levels of 112 dB at 0 dBFS (even louder). However, if peak playback levels are set at 120 dB SPL (painfully loud) at 0 dBFS, the NS3™ noise characteristics will become objectionable and NN3™ would provide better results.
NN1™, NN2™, and NN3™, NS1™, NS2™, and NS3™ are trademarks of Benchmark Media Systems.
UV22™ is a trademark of Apogee Digital.
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