Moderators: Dave Moll, Andrew Davie, Steve Anderson
Stephen wrote:I agree wholeheartedly, Steve.
AncientBrit wrote:...And we normally drive a CRT from a voltage source.
Graham
AncientBrit wrote:Very neat Steve, certainly a new approach.
Graham
AncientBrit wrote:Jeremy Jago demonstrated an interesting concept at a recent convention.
Graham
Similarly, our ears are logarithmically sensitive to sound, being able to distinguish subtle differences in intensity at low levels but hardly at all at higher levels. Likewise for audio systems, spurious noise due to the recording or transmission medium is more noticeable than if our ears had a linear response curve.Klaas Robers wrote:Our eyes are sensitive to the ratio of light. So the cantrast of brightness 1 in respect to 2 is equal to the sunjective contrast between 4 and 8. And also between 0,1 and 0,2 !! This implies that noise in dark areas is much more visible than noise in bright areas.
Gamma correction does the opposite. It amplifies the dark video signals and attennuates the bright video signals. Then it is transmitted. Equal noise is added. The picture tube attennuates the dark video signal, so attenuates the added noise and amplifies the bright video signals. That amplified noise is no problem at all because our eyes are insensitive to it.
Yes, Klaas, I agree that more sophisticated compander systems have a slow-responding amplification gain change to minimise intermodulation distortion. The DBX system is an example. However simple companders are simply non-linear amplification systems. For instance, a super-regenerative detector has such an instantaneous compression characteristic to provide an "automatic volume control"-like action. That is why super-regenerative detectors always have a high level of background noise. They amplify low levels much more than high levels.Klaas Robers wrote:Oh no Stephen, gamma correction is totally different from compression/expansion. With compression/expansion the amplification changes (slowly) with the loudness of the audio on a certain moment. On a certain moment the amplification of the compressor and/or the expander is almost constant. This is to eliminate intermodulation.
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