I wonder if a test of standard cell phones or satellite phones would prove better in near space than current in use technology? I do find it hard to believe that we can't get reasonable audio quality from space. If the limitations are mic and front-end electronics could we just upgrade that part and realize new and improved audio performance? Just a thought..
Rich, it strikes me as naive for the diyAudio guy to believe that the audio should be good in the first place. We've been softened up by the ready availability of fantastic quality audio in our daily lives. The radio links from spacecraft have to operate in an abysmally low SNR environment. Fidelity is an irrelevant luxury; extracting intelligibility from this channel requires much time- and frequency-domain processing and filtering. You could probably get better audio from near-Earth craft with systematic redesign, but what's the incentive? NASA doesn't want to rummage around for different receiver types for craft at different distances from the earth.
Recovering signals from distant spacecraft makes anything in even audiophile audio look simple (and I'm an audiophile, don't get me wrong). Last time a signal from Pioneer 11 was picked up, the ratio between the size of the antenna and the distance away was around 4 trillion. That's a path loss of 252dB. In a hifi system, that would be like trying to measure a signal difference caused by _one_ extra electron arriving _per day_...
There really is no excuse for it. Clear communications is desirable and necessary. There is no technological reason, analog, digital or rf that the communications can't be crystal clear. NASA hasn't bothered probably more for marketing reasons than anything else. But whatever the reason they haven't bothered, it is technically feasible, not very expensive, and clear audio should be designed into the system. If all they have is Monster Cable audiophiles at NASA, let me know and I'll design every aspect of a high quality system for an appropriate price.
It's obvious as to "why": it makes it sound more realistic, not faked. If it sounded too good, people might think the astronauts were next door, in a studio, and the whole thing was a fake set-up--the equivalent of being Photoshopped. ;-)
I suspect it's a very narrowband, companded, low bitrate channel, and the reasons for it not being better are directly related to the prioritization of video quality over audio quality.
After all, the audio is just human voice and the only fidelity criteria is intelligibility of speech. Pictures and video, on the other hand, are what make space exploration interesting to the public and therefore have much greater PR value to NASA.
I like the third alternative -- or one very similar to it: The audio SOUNDS different from other audio broadcasting; so, listeners can tell when the words are coming from space or not.
NASA might as well make it sound degraded, because sometimes distant communications do get degraded.
OK, let me get this straight. Satellite phones use an array of orbiting repeaters. The ISS is orbiting the same planet.
I would think the shortest distance would be a line between the astronaut and the satellite, just tap in.
By the way, digital answer machines compand the living daylights out of your voice and it still sounds good, even over the bandwidth limited POTS lines.
AND, if the navy seals can use throat mikes for covert ops, the technology is already there.
TDRS...was a 70's design and we did not think about HD video at the time. We just launched a new gen TDRS Sat - I think in the last 36 months or so. We should see a better mix between audio and video in the next few years. Given the current Administrations idea that it is more important to reach out to the Muslim world via NASA...we may never get a full upgrade to TDRS. I also look for manned exploration to get hit big..at least for the next 2 years.
Nasa spinoffs have created a great world to live in. We need this kind of exploration to continue the pace of innovation we have become used to.
The shuttle is based on 1960s technology with periodic upgrades to systems like avionics. As long as Houston has its telemetry down links, I doubt they worry much about audio quality. Remember, also, that many of the Apollo astronauts were amazed at how good comms was during lunar trips. About the only time there were problems with voice communications was during maneuvers like extracting the LM from the Saturn third stage en route to the moon. NASA has bigger fish to fry (like developing heavy-lift rockets) than upgrading audio.
Even if you designed every aspect of a high quality system for _FREE_, they would not upgrade it. The cost of the documentation alone is prohibitive. It's not for technical reasons, but bureaucratic. Stop thinking like an engineer :-)