What is Automatic Gain Control?
An audio tape generates a certain amount of noise. If the level of the signal on the tape is low, the noise is more prominent, i.e., the signal-to-noise ratio is lower than it could be. To produce the least noisy recording, the recording volume should be set as high as possible without being so high as to clip or seriously distort the signal. In professional high-fidelity recording the level is set manually using a peak-reading meter.
If high fidelity is not a requirement, a suitable recording level can be set by an AGC circuit which reduces the gain as the average signal level increases. This allows a usable recording to be made even for speech some distance from the microphone of an audio recorder. Similar considerations apply with VCRs.
The disadvantage of AGC is that when recording, say, music with quiet and loud passages, the AGC will tend to make the quiet passages louder and the loud passages quieter, reducing the dynamic range and losing musical quality.
Most reel-to-reel tape recorders and cassette decks have AGC circuits. Those used for high-fidelity allow it to be overridden manually.
Most VCR circuits use the amplitude of the vertical blanking pulse to operate the AGC. Video copy control schemes such as Macrovision exploit this, inserting spikes in the pulse which will be ignored by most television sets, but cause a VCR's AGC to overcorrect and corrupt the recording.
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Enable Automatic Gain control:
if checked iSofter Audio Recorder Vista will use this dsp when recording.
this feature can let's some song get a same volume