Quote:
Originally Posted by Dazrin
Ya, it's pretty common to hear well above 20k Hz up until sometime in your 20s. A little later sometimes.
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No, nothing like as high as that. It's rare that young people can hear as high as 18 kHz, though a very few can hear up to 28 KHz. Hardly any adults can hear much above 16kHz.
Also actual program material has little above 10 kHz, which is why that was chosen in 1934 for 405 TV audio upper limit. You can use a cheap electret microphone which is good to about 18 kHz and has some response to 50 kHz and connect it to a professional spectrum analyser that does over 150kHZ on the lower range. There is little content above 8kHz and you'd struggle to exceed 15 kHZ with harmonics (overtones) of instruments in a significant level. The telephone system is up to about 3.5 kHz and most codecs for mobile or VOIP sample at 8 KHz, thus the filtering at the input has to roll off before 4 kHz. AM Radio used to be up to about 6 KHz, but channels are now 10kHz or 9 kHZ depending on region and as it's AM the maximum audio frequency has to be less than half. Typically a 4 to 4.5 KHz filter. FM audio has traditionally been anywhere from 10 kHz to 16 kHz. 19KHz was chosen as stereo pilot and 38 kHz for the L-R signal, thus the mono L+R and and the subcarrier L-R both must have no content at 19 kHz. Filters can't be like a cliff. Hence 15 or 16 kHz
The TV whistle is less than 16 kHz for 625 or 525 line systems. Magnostriction on ferrite cores. Originally 15750 Hz for 525 lines, 15625 for 625 lines (Both predate colour)
441 25 fps / 50Hz was 11025 Hz
441 30 fps / 60Hz was 13230 Hz
405 25 fps / 50 Hz was only 10125 Hz and very obvious.
819 25 fps /50Hz was 20475 Hz
1125 lines is Analogue HD origin of current 1080 lines.
Basic VGA or Progressive analogue from NTSC DVDs is a 31500 Hz line frequency.
Some TVs even in 1950s had no line whistle due to construction of the LOPT and scan coils.