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In the first seconds of this video you can see/hear ISS astronaut Samantha Cristoforetti prepare for a PR event:

During the preparation she uses two different microphones. A small, blue box-like one for communication with mission control, and a larger, cylindrical one for talking with the interviewer. The latter has a much superior voice quality.

Having two different microphone systems on the station seems quite redundant. Why don't the International Space Station (ISS) astronauts always use these high quality microphones?

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    $\begingroup$ It might not be the actual microphone but the radio channel used that limits voice quality in order to save on transmitter power and bandwidth. $\endgroup$ – rackandboneman Dec 6 '16 at 13:09
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That blue box is a wired receiver unit for the wireless microphone (they currently use a Sennheiser handheld with SKP-100 wireless transmitter, but they did or still do use also products from other companies, inc. e.g. Shure that I know they flew during some STS missions to the station). The box also hosts its own microphone because the wireless microphone does need charging (EPO - Education & Public Outreach events usually last about half an hour or less, while they're in contact with CAPCOM throughout the working day on the station and the small battery pack it has wouldn't last that long without requiring a few battery swaps) and it might be awkward to use in some circumstances and not having to worry about a free-floating microphone might be easier too. For example, here's Karen Nyberg speaking into a microphone while conducting a session with the Advanced Colloids Experiment in the Destiny laboratory:

   enter image description here

     NASA astronaut Karen Nyberg speaks into a microphone while conducting a session with the Advanced Colloids Experiment
     (ACE-1) sample preparation at the Light Microscopy Module (LMM) in the Fluids Integrated Rack/Fluids Combustion Facility, on
     June 24, 2013. Image: NASA

The box has two large buttons that while I can't seem to find any supporting document to their purpose can really only be to toggle the wired and wireless microphones on and off and adjust their volume during communications with CAPCOM (Capsule Communicator):

CAPCOM communicates through the use of voice loops (collections of audio communication from individuals which are tied together on an intercom through a satellite link). CAPCOM also coordinates crew communications with other spacecraft communicators supporting the mission which may be in other locations - such as Huntsville, Alabama; Munich, Germany; Tskuba, Japan or Moscow, Russia.

Here's a photo of Shannon Walker on the station showing the box with the two buttons and a microphone behind her a bit better:

   enter image description here

     NASA astronaut Shannon Walker, Expedition 24 flight engineer, is pictured near a robotic workstation in the Destiny laboratory of
     the International Space Station. Credit: NASA, Source: Wikimedia Commons (click for higher resolution)

So in the video you link to, Samantha Cristoforetti would first have to reach for the receiver unit to enable both microphones to pass through the intercom voice loop anyway. But in majority of cases, having watched quite many public events from the station (available either live on NASA TV or recorded on NASA YouTube channel), station astronauts would mostly use the better quality wireless microphone.

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  • $\begingroup$ One interesting tidbit, today's spacewalk #31 (Wilmore and Virts) CAPCOM officer is Suni Williams. Currently live on NASA TV. Also see our schedule for other events that might be of interest. Cheers! $\endgroup$ – TildalWave Mar 1 '15 at 15:59
  • $\begingroup$ NASA wears their best in those dog and pony shows they put on for the public (and politicians). When they're just doing their job, they use the lesser quality microphones, lesser quality video (or no video). Those dog and pony shows means some satellite data or someone's experimental data is not being downlinked. TDRS bandwidth is a finite resource. $\endgroup$ – David Hammen Mar 1 '15 at 21:45
  • $\begingroup$ @DavidHammen Dunno, Sam Cristoforetti used that blue box wired mic all the time during the three recent (including today's) spacewalks as the third / support crew and they were nearly all day long events with live public broadcasts. It just wouldn't make much sense to use the wireless because it would run out of juice and be rather awkward with Sam also being on notebook all the time. And surely a parade horse like the ISS would have allocated TDRS time and which microphone they use doesn't really change sat link time or bandwidth, does it? $\endgroup$ – TildalWave Mar 1 '15 at 22:50
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    $\begingroup$ The real point is that they don't use bandwidth frivolously. If they're doing a PAO event, they'll use a high data rate connection. If they're doing critical operations, like EVR or EVA, they'll use at least high data rate video. For operational purposes, high quality audio adds no value and it takes away from other bandwidth customers, both on ISS and other TDRS users. $\endgroup$ – Tristan Mar 6 '15 at 22:59
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    $\begingroup$ @TildalWave The blue box is called a BPSMU (Battery Powered Speaker Microphone Unit), pronounced "bipsmoo". The two buttons are XMIT (Transmit) and ICOM (Intercom). $\endgroup$ – Organic Marble Aug 30 '17 at 17:35
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The high-fidelity microphones (as used in broadcast media, for example) are all about relaying the highest quality sound signal, and may compromise other aspects such as reliability, tolerance of extreme environments, battery life, etc. because the primary market for them can accommodate their limitations one way or another.

On the other hand, in space, reliability is king, along with minimizing weight. Mission control doesn't need to hear music from the ISS; as long as the microphone can reliably convey an intelligible speech signal, that's all that counts.

Hi-fi mikes are good for music (any decent one should handle something like 20Hz-20kHz, a typically quoted range of human hearing); the useful information in human speech is conveyed in a band from 300Hz-3kHz. Frequencies outside that band can be completely removed from a sound signal and we can understand the speech content within it. Getting good reproduction over 20-20kHz is not that easy, and a mike which can do it will probably need to be handled with some care. On the other hand, mikes capable of speech bandwidth can be made relatively easily and can be quite robust.

For everyday communications, and especially when it's just got to work, the lower-fi higher-reliabilty mikes would win out. When it's a press event, makes sense to bring out the media mike, with the hi-rel always there to back it up.

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    $\begingroup$ Not entirely convincing. Yes, the condenser microphones used in broadcasting / music studios are fragile and need phantom power supply, but the standard microphone for voice (both sung and spoken) in live concert applications remains the Shure SM-58, a completely passive and tank-like robust design from the 60s that still sounds easily as transparent as the “good” mic in the linked video. Of course the SM-58 might be considered too heavy, but there are also very light, sturdy and still pretty high-quality electret condenser microphones available. $\endgroup$ – leftaroundabout Mar 1 '15 at 21:07
  • $\begingroup$ "the useful information in human speech is conveyed in a band from 300Hz-3kHz". Not that simple. As an experiment, at work I digitally filtered a speech signal, removing pretty much everything under 1 kHz and lots of the signal under 3 kHz. It was surprising how easy it was to follow the speech afterwards, with the "theoretically useful" part filtered out. The reason: the human ear will fill in missing fundamental tones when sufficient harmonics are present. $\endgroup$ – MSalters Mar 2 '15 at 0:05
  • $\begingroup$ @MSalters I won't disagree. The 300-3kHz range I cited was a typical guideline I remember from my coursework and subsequent exposure to the telephony industry. POTS filtered to that band. I suppose it guaranteed intelligible speech and allowed for minimal cost in terminal, switching, and transmission equipment. $\endgroup$ – Anthony X Mar 2 '15 at 0:16
  • $\begingroup$ It's indeed a remnant of the old analog telephone network. 300-3000 is sufficient but not necessary. However, the old analog electronics could not guarantee decent SNR above 3 kHz or below 300 Hz so that was simply filtered out without a loss of intelligibility. The low band especially was needed to prevent 60 Hz interference. $\endgroup$ – MSalters Mar 2 '15 at 13:05
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Pure speculation on my part.

To anybody not habituated to listening to radio communication, static/radio-interference may necessitate multiple 'takes'. This may be the case with the majority of viewers. The larger microphone probably carries some on-board signal processing, and high-gain instrumentation. In short, investing in the microphone potentially helps keep down the cost of the PR (+:

On the other hand, mission control probably communicate over the radio day-in, and day-out. They can do without the overheads mentioned above.

p.s. As I said, pure speculation. Feel free to down-vote!

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