I remember being very disappointed in the Sennheiser noise cancellation headphones for in-office work because they cancelled the droning of ventilation and computers and air conditioning and the like, so when you put them on it's like being under water, but they didn't cancel human voices all that much. In fact, project managers on the phone, people mentioning my name, questions related to the project I was working on – it all stood out, now. My interpretation was that this sort of noise cancellation was optimized for noisy workplaces where you still needed to hear your colleagues. Like (military) airplanes, for example. Which is exactly what I hate the most.