iBasso D16

iBasso build a 1-bit DSD DAC into D16 because there's zero error at the point of conversion. There, D16 relies on the total accuracy of DSD's 1-bit conversion to analog, taking advantage of DSD's sheer ease of decoding to boot.

The pitch for DSD's 1-bit conversion is digital at its simplest and closest point to analog – level represented only either as a 1 or a 0, switching on or off. To achieve analog, the bitstream is simply low-pass filtered.

But there's work D16 needs to do first, preparing incoming DSD and certainly PCM data from your smart devices over USB, coaxial or optical inputs to emerge as the best possible 1-bit digital stream for conversion.

How D16 alleviates said white noise issues of DSD64 – indeed, of any inherent problems to single-rate material be it DSD's noise or PCM's steep digital filtering, intersample overs and digital pre-emphasis – is that it applies heavy oversampling to incoming data. 

iBasso's DSP oversamples data to huge bit depth and sample rates synchronous to their new FPGA-Master 2 generating I2S. The new multibit data running many times DSD's base 2.8Mhz rate is then put through a Pulse-Width Modulated (PWM) process in preparation for 1-bit decoding. 

iBasso treats each of D16's 32 0.1% resistors per DAC phase as individual entities, operating them at very specific moments in the time domain. Ordinarily that might spell chaos co-ordinating a total count of 128 individual DAC elements, but it's iBasso's FPGA-Master 2 that grants a firm grip of how each resistor-capacitor low-pass filter outputs in the time and frequency domain.

The result of the entirety of 128 DAC elements outputting at phased intervals leads to a coherent, continuous waveform with finer stairsteps in time. That captures more detail in your music and reduces errors, decoding your music back more accurately to the original waveform.

D16's PWM DSP pre-stage addresses the problems of conventional noise-shaped digital's inconsistent rise and fall edges at the frequency level, with adjustments made to facilitate more accurate, predictable switching. A digital volume control with large coefficients is also added here to trim levels and add datastream width.

This approach results in a reduction of errors by avoiding intersymbol interference. Notably, non-linearities arising from rise and fall mismatches do not manifest as total harmonic distortion. iBasso's PWM DSP does not produce harmonic errors that vary with digital output levels.

This high bit and sample rate headroom is free from overload issues when it is eventually brought back down to the required 1-bit DSD signal for low-pass filtered conversion – but now at a bandwidth of 49Mhz, moving DSD's white noise issues far, far out of the audible band.

iBasso's discrete proprietary tech immediately differentiates itself from commercial DAC chips, where IC packages are often too small to perform an ideal 1-bit DSD conversion. D16 also avoids the errors of dynamic element matching inherent to 2-7 bit delta-sigma decoders.

The delicate analog voltage waveform painstakingly decoded from DSD in D16 is precious. iBasso's R&D, invested building their own DAC, pays off as the fragile small-signal goes on to be volume adjusted by the same discrete resistor attenuator of DX320 Max TI fame.

Said stepped attenuator preserves the resolution of D16 at any listening level. It's that that enables it to play it delicately into your flagship earphones for enjoyment at realistically lower volume levels.

Because, it's easy to play it loud, but everyone knows it's in playing back tiny sounds that is the litmus test of a powerhouse capable of outputting as much volume as D16.

Without resting on past laurels to increase and decrease both signal and noise levels together at the same time – as only an analog volume control can – iBasso went for the jugular here. After years of work, Head-Fi's analog specialists have once again applied their own, proprietary, stepped analog volume control here to great effect.

Transparent at any volume setting down low as much as up high, with virtually perfect +/-0.1dB channel-matching, this iBasso behemoth exposes detail buried deep around the noise floor of your music.

So begins D16's fully-balanced, true differential analog circuit that runs at a massive 13 volt operating voltage for linear open-loop operation. Its power stage is fully discrete and boasts buffers capable of outputting more amperes of current than is needed in reality. Said power stage is another call for iBasso's Super Class A to appear.

Current mirrors ensure D16's push-pull operation works without crossover distortion, yielding Class A-like performance at all power output levels. That makes for extremely linear open-loop operation before negative feedback is applied ... yet mostly avoids the heat and inefficiency typically associated with Class A designs.

Certainly, the quality of D16's power is not discussion, and will reproduce the fidelity of its 1-bit DAC – a milestone in iBasso's history – into your full-sized transducers of choice via your laptop or desktop's USB in your office, or your smartphone on business travels.

With superb damping factor as a voltage source, enough standing bias current and signal-to-noise performance to follow today's flagship IEM impedance down low, you know PB5 will be even more in its element pushing TOTL headphones.

Everything from Focal to a Fostex and Rosson Audio Designs plus Yamaha and ZMF Headphones is applicable. If you want to free yourself from USB's tether, check out the rest of iBasso's self-contained Android music players here, or view all our other DAC/amps here.