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I was reading about Audiotechnica's new "Pure Digital Drive" headphone drivers here, and I can't understand how their drive scheme would be better than having a regular DAC feeding into the voice coil. It seems like the first curve they show, 'Analog Input to Driver' provides a smooth interpolation between the signal that would be more desirable than a choppy digital transition like they show in their 'Digital Output' waveform. I know the specifics of their technology is proprietary, but I was wondering if anyone here could better explain why this scheme is a good idea.

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  • \$\begingroup\$ no noise, at any stage \$\endgroup\$ – dandavis Aug 30 '17 at 22:49
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    \$\begingroup\$ This is simply bullshit because D→A conversion does not sample a signal. \$\endgroup\$ – Janka Aug 30 '17 at 22:54
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    \$\begingroup\$ Support for all the compresssion codecs is the secret sauce with marketting BS \$\endgroup\$ – Tony Stewart EE75 Aug 30 '17 at 22:56
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    \$\begingroup\$ Think about how a Class D power amplifier works. Modulated PWM signals that are then filtered and fed to the load. And not a single DAC in sight. Not saying that is what they are doing, just pointing out that you don't need a DAC to convert a digital signal to analog. \$\endgroup\$ – Dwayne Reid Aug 30 '17 at 23:07
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    \$\begingroup\$ It sounds like they are just feeding PDM signal (Pulse Density Modulation) directly to the voice coil and having the voice coil and diaphragm mechanically filter the PDM signal into a smooth analog "waveform". Same stuff as the "1-bit DAC". I found a nice paper that's an easy read here if interested: users.ece.utexas.edu/~bevans/courses/rtdsp/lectures/… \$\endgroup\$ – Vince Patron Aug 31 '17 at 0:03
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There is a DAC driving the coils, it's just that it's a 2-level DAC that works as a class D amplifier. The difference between 'digital' signals and 'analogue' signals is that in the former, we don't care about the exact levels, or whether the levels change a little between pulses. By that definition, this headphone drive system uses analogue signals, the digital to analogue converter must be consistent in the levels it provides to the coils.

A lot of what is written in that note is pure BS and audioFUD. However the technology works, and works sufficiently well in terms of audio that the differences between that and conventional good DACs are swamped by other considerations. Being class D, they will (should) be lower power consumption than a more conventional signal path.

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  • \$\begingroup\$ Re: "this headphone drive system uses analogue signals", it's vague but I don't think that's what the marketing wording is saying. In a Class D amp or when you're doing PDM you are driving the speaker digitally. It's just that you're relying on the speakers inductance and the mechanical inertia to smooth out and filter the digital pulses to an "analog average". Similar way when you PWM an LED. The LED is blinking full on and full off digitally but your eye is doing the filtering to perceive an average light intensity. \$\endgroup\$ – Vince Patron Aug 31 '17 at 18:17

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