Is the sound of pulsars converted radio waves, or actual sound that's has been put into a loudspeaker? Do neutron stars produce sound?
In the answer to the above question, it has been mentioned that:
'The pulsar signal is often transformed directly into an audible signal by simply feeding it to a loudspeaker.' But as far as I know, the sound that we hear from the pulsars are radio waves that have been converted into audible sound waves. Someone even asked him about radio waves, and he replied, Radio pulsars have rotationally modulated radio emission. Is this guy right?
Or perhaps my understanding is wrong? I need some clarification.
 A: The examples I have seen (heard) are where you essentially feed the signal (obviously converted into some electrical voltage) into a loudspeaker (or simulation of a loudspeaker).
Thus you get an audible "click" from a pulsar pulse, associated with the rapid rise and fall of the signal, that produces frequencies in the audible range. Similarly if a pulsar spins 100 times every second, then the clicks will merge to give a constant drone at 100 Hz.
The wavelength at which the data from the pulsar is received is not particularly relevant. Many radio pulsars can actually be seen to pulse at other wavelengths too, including the optical (e.g. the Crab pulsar). In principle these signals could be converted into a similar audible sound.
A: Look at the Parkes Observatory website, or here. Radio signals from radio pulsars can be demodulated into audio signals: this is what the radio in your car/house does, you just need a big antenna to get the radio signal (i.e. a a radio telescope). Since the pulsar is a rotating neutron star that emits a beacon, the pulsar sound has the periodicity of the rotational period of the neutron star (i.e. a "neutron star day"): yes, radio pulsars have rotationally modulated radio emission, so "that  guy" is right.
More technically: rather than simply look at graphs of the radio power emitted by a pulsar against time, it is possible to feed the digitised signal into a sound card and listen to the sound of a pulsar. What we hear is the regular clip of the pulsar flash superimposed on the background  made up of receiver noise plus astrophysical background (from the interstellar medium plus cosmic microwave background). This wasn’t a sound originally, it’s the brightness of a radio signal turned into a sound, similar to AM broadcasting.
If you are interested in sounds from space, this website is really nice.
A: Here is the spectrogram of the Vela pulsar taken over a duration of 1 second.

P.S: I apologise for not adding labels. The y-axis represents frequency, the x-axis the time, and the "brightness" represents the intensity of a given frequency at a given time instant.
So what you hear when "listening" to a pulsar is the data used to make this spectrogram being played out at a suitable sampling rate. As you can clearly see, this spectrogram has around 10 "slashes" or pulses. Each of these pulses will correspond to a clicking-like sound when you listen to it.
As an interesting exercise, I encourage you to use the data at https://drive.google.com/file/d/0B71z6CTGT4maU2JUY18yWFM2SU0/view?usp=sharing, convert it to an audio signal and try listening to it.
