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I have a model 224 I picked up and I don't actually know how it is supposed to function nor what it is supposed to accomplish. Thanks; Norm
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The 224 and 224ds were noise reduction units that were meant to be ran in line with a cassette or open reel tape machine. They also included a dbx disc decoder for (obviously) dbx encoded vinyl LPs.The manufacturer's claim was for up to 80 db of noise reduction...
I still have one in my rig as well as a 1bx for expanding the compression of FM radio...
"David! You can KILL a man with a chopstick!" -Keith Charles, Six Feet Under
dBx compresses the music in a process termed 'companding', or compression and expansion of the processed signal (music.) The process causes the noise and tape hiss to become 'masked-out', probably like a subnet-mask does with an IP address. The noise goes when the signal is expanded. Therefore.. an improvement in the signal to noise ratio. In other words, on a dBx LP.. it's very good practice to lower the volume before lowering the stylus, especially on dBx recordings, saves the speakers! dBx LP's are a good treat with a stand alone dBx decoder.
yes, and any frequency responce errors during disc decoding (cartridge, riaa eq) or tape playback (alignment, bias) will be magnified as well.It was a great idea at the time (mostly PRE digital) but had its inherent flaws as well...
I wish I could find a service manual (not pay for it, just find one...)
for the 224 and 1bx...
"David! You can KILL a man with a chopstick!" -Keith Charles, Six Feet Under
Yes, that's what it does, more or less. Before recroding, the dynamic range of the signal is reduced (compressed) by a nonlinear amplifier. That makes the quietest signal louder and the loudest signal quieter. That keeps the signal further away from the noise floor and further away from saturation.On playback, the signal is expanded by another nonlinear amp with a characteristic complementary to the compression amp's characteristic. That's where the term "compander" comes from -- COMpress/exPANDER.
One drawback is that any distortion that occurs between compression and expansion by the tape electronics, the tape, anything in the LP chain, etc., is multiplied by the expander. So you get more dynamic range at the expense of some added distortion.
Another problem is that as the quietest passages change loudness, the noise floor "pumps" noticably and annoyingly.
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