Lock Range Adjust is actually a really cool feature, it refers to the adjustment of the PLL (Phase Locked Loop, every dap has one) which is composed of the crystal oscillator (aka clock) timing the digital signal (aka I2S) to the DAC for conversion to analog. So the Lock Range Adjust is letting you change a parameter for the timing of the digital signal to the dac, which creates differing sound, no setting is better than the other, it is completely personal preference. It is not a gimmicky software feature as it does not degrade the SQ, it is a parameter adjustment in the digital stage which interacts directly with the PLL which gives us a degree of control over the digital stage of the dap, probably wasn't easy for Onkyo to implement! No other dap has implemented this feature, so kudos to Onkyo for innovation.
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