I’ve seen statements like this here as well as on other Bluetooth headsets like the Bose nc700. I have a hard time understanding how this works. Do the headphones use an ADC to put the voltage back in the digital domain, then apply DSP and output the result with its built-in DAC? Or is DSP being used as shorthand for active amplified alteration of signal?
In the case of the N700NC M2, it depends whether it is "on" or "off":
- Wired + Off = no BT, no DSP (equivalent to a regular wired HP)
- Wired + On = no BT, DSP active (ANC, ambient/talk-thru button, but no EQ). White led (blue led when BT is connected).
There is no sound for ~1s when you switch between on & off with the wired audio cable connected. If "on", connecting/disconnecting the wire from the HP side (whether it is connected to something on the 3.5mm side does not matter) disconnects/connects the Bluetooth, but has no effect on the DSP. It means there is a jack-presence detection and I assume the source signal is digitalized through an ADC: there is audible difference (volume and sound quality I think) between [Wired + Off] and [Wired + On]. It could be due to the ADC limitation or the DSP processor.
The USB-C is only for charging. Connecting the cable turns off everything: BT, DSP, wired connection. There is no way to listen to anything when charging.
That whole "logic" is very similar on the Mark Levinson 5909 (which makes me think the two are probably related...), with a few differences: the 5909 wired audio cable is going through the USB -C connector and the 5909 has a digital USB mode that is not available on the N700NC M2.
Amir tested the N700NC M2 wired and "on". As he indicated, any DSP correction would be active. In the case of the N700NC M2, that would mean ANC and, if enabled, ambient/talk-thru mode, but no EQ. This could be a problem for the measurements... For example, the ANC processing has a time-element factor (like a PID-type response). This could very well explain the difficulty Amir had to match L & R channels and the choppy FR response...