Some knowledgable folks have asked why the AD-20 doesn't dither its least significant bit, considering that it truncates its 20-bit data down to 16-bits. (In some situations, truncation results in audibly unpleasant artifacts.)

Although the AD-20 uses a true 20-bit A-to-D converter chip (AKM5351, a slight improvement from the AKM5350 found on the ADA1000 converter), its actual dynamic range is just around 98dB. This means that although there may be more signal in the noise, the S/N ratio is really only giving you about 16.5 bits of real information above the noise floor. Oddly enough this works to our advantage when used with 16-bit gear (like CDs and DAT decks) because there is already a natural 'dither' in the 16th bit as it is being recorded from the AD-20. There is no need to add additional dither noise to the signal because the signal is already hanging right off the edge of 16-bits.

If the AD-20 truly delivered 20-bits of real information (that would probably require a so-called 24-bit converter!) then a 20-bit to 16-bit truncation would result in the quantization noise that the human ear would find offensive. In this case, an A-to-D would require additional dither noise to be added just beyond the 16th bit to randomize the signal such that the 16th (truncated) bit was not perfectly quantized.

Summarizing, the AD-20 will sound great with your 16-bit DAT or MD recorder due to the natural dither in the A-to-D converter. And if you go through the effort of capturing 20 or 24-bits (e.g., with a Zefiro ZA2 in a digital audio workstation) then you'll still gain a few extra dB and perhaps a bit more signal below the noise floor.

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