Re: Equalization ??
Doug, I looked at the links in your post and probed around that web site some. I couldn't find the references to constant signal velocity type equalization. I wonder where you found that?
I am not an expert on audio recording so this is just my opinion but here is what I get out of the discussion on that site. The early simple cutting heads were driven by an open loop amplifier and the velocity (in the axis of signal motion) was proportional to the amplitude of the signal. This means that for a low frequency signal (say 200Hz) the actual distance of the cutting head travel would be greater than it would be for a higher frequency signal (say 500Hz) even though the two signals had the same amplitude. This means that as the frequency of a recorded tone continues to get higher, the physical excursion of the cutting head gets smaller and eventually gets so small that it approaches the size of imperfections, granularity of the media and also of dust and impurities that may be picked up after the cutting. To get around this limitation of high frequency cuttings being down in the noise level, an electronic boost was given to the signal prior to applying to the cutting amplifier. Also to limit the low frequency excursion from cutting into the adjacent groove, an electronic attenuation was applied to the bass signal. The end result of all of this, if you look at it from the stand point of the size of the signal excursions on the groove, the best you could hope for would be constant amplitude excursions of the cutting head at any audio frequency for constant level input signals. This is referred to on some articles as "constant amplitude recording". To achieve this you have to attenuate the bass and boost the highs prior to applying the signal to the cutting head amp. If you play such a recording with a perfectly flat playing system, you won't hear much bass (because it was attenuated) and the highs would be overly loud because they have been boosted by the equalization curve to keep them from becoming so small that they would be overwelmed by the noise created by the miroscopic bumps or dirt in the groove of the recording. To account for this on playback, you need to boost the bass and roll off the highs above a certain frequency at 6DB per octave. After you do this you should have achieved a "flat" or true reproduction of the audio signal that was originally picked up by the recording microphone. I think that this really what was meant by the terms constant amplitude and flat. Maybe this helps? Maybe not.
John
Doug, I looked at the links in your post and probed around that web site some. I couldn't find the references to constant signal velocity type equalization. I wonder where you found that?
I am not an expert on audio recording so this is just my opinion but here is what I get out of the discussion on that site. The early simple cutting heads were driven by an open loop amplifier and the velocity (in the axis of signal motion) was proportional to the amplitude of the signal. This means that for a low frequency signal (say 200Hz) the actual distance of the cutting head travel would be greater than it would be for a higher frequency signal (say 500Hz) even though the two signals had the same amplitude. This means that as the frequency of a recorded tone continues to get higher, the physical excursion of the cutting head gets smaller and eventually gets so small that it approaches the size of imperfections, granularity of the media and also of dust and impurities that may be picked up after the cutting. To get around this limitation of high frequency cuttings being down in the noise level, an electronic boost was given to the signal prior to applying to the cutting amplifier. Also to limit the low frequency excursion from cutting into the adjacent groove, an electronic attenuation was applied to the bass signal. The end result of all of this, if you look at it from the stand point of the size of the signal excursions on the groove, the best you could hope for would be constant amplitude excursions of the cutting head at any audio frequency for constant level input signals. This is referred to on some articles as "constant amplitude recording". To achieve this you have to attenuate the bass and boost the highs prior to applying the signal to the cutting head amp. If you play such a recording with a perfectly flat playing system, you won't hear much bass (because it was attenuated) and the highs would be overly loud because they have been boosted by the equalization curve to keep them from becoming so small that they would be overwelmed by the noise created by the miroscopic bumps or dirt in the groove of the recording. To account for this on playback, you need to boost the bass and roll off the highs above a certain frequency at 6DB per octave. After you do this you should have achieved a "flat" or true reproduction of the audio signal that was originally picked up by the recording microphone. I think that this really what was meant by the terms constant amplitude and flat. Maybe this helps? Maybe not.
John
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