Jonathan Richards wrote:
On Thursday 12 Feb 2004 5:31 pm, David Luff wrote:
OK, here's some instructions on how to generate new ATC voices for
FlightGear. Hopefully this will make some sense to somebody, ask if it's
unclear.
<snip>
Two files are required for each voice - a wave file containing the actual
sounds, and an index file that basically describes where in the wave file
buffer to find each word or phrase. The current voices for the ATIS can be
found in $FG_ROOT/data/ATC and are called default.wav and default.vce for
the wave and index file respectively. Note that one important change will
be made in default.vce - currently it is indexed by byte position into the
sound buffer, but I've decided it would be better to index by time into the
buffer, since that is more robust to changing the recording quality, and in
the future possiby using encoding such as Ogg Vorbis. Also, the first line
currently contains the number of subsequent lines, but I think that can be
ditched!
<massive snip>
David
In what units shall the time index be specified? The sampling rate sets a
resolution limit on the timing, so for 8kHz we only need 1/8000 sec = 125
microseconds precision, but if we have an ambition for higher rates, we need
more. [1]
In reality, radio comms are not HiFi standard. Does anyone know what the
typical bandwidth is? Or should we simulate by taking a beautiful 22kHz
recording and filtering it to sound like the real thing? Perhaps as an
option, so one can do radio practice with bell-like clarity at first, and
graduate to crackly reception of foreign languages and accents later!
Regards
Jonathan
[1] It occurs to me that for chunked formats like WAV, there is a mathematical
relationship between the byte position and the time offset which could be
used for conversion, no?
Does anyone know, does Plib include realtime sound mixing, downsampling
and volume control (the sound should be downsampled to match the real
aircraft comms, it should be more soft when you're further away from
the transmitter and we should mix some noise sounds with a speech to
sound everything more like in real life).
- Matevz
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