dbx 128 Instruction Manual Download Page 4 | Manualshive

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Summary of Contents for 128

Page 1: ...MODEL LEVE ee BELOW 220vE a dbx Il 128 DYNAMIC RANGE ENHANCER 7 NOISE REDUCTION SYSTEM i Cc x a ABOVE cs THRESHOLD Poe 4 ad cee YP X 5 R3 0 RRE post REC B Ss 5 0 eek 7 10MV a ES DYNAMIC RANGE J dbx E...

Page 2: ...e also covered The remainder of the 128 Operator s Manual is a detailed set of connection diagrams operating instructions and explanations of the 128 s functions WARNING TO PREVENT FIRE OR SHOCK HAZAR...

Page 3: ...r ex pansion begins when the ABOVE THRESHOLD LINEAR switch is in the ABOVE THRESHOLD position When the ABOVE THRESHOLD LINEAR switch is in the LINEAR position set the LEVEL control so that ABOVE THRES...

Page 4: ...WY PLAY OUTPUTS Connect the cables RECORD INPUTS For connec RECORD OUTPUTS from these outputs to the tape play tion of the cables from your Connect the cables back input preamp input or tape preamp s...

Page 5: ...PE 2 Press the 128 s TAPE REC and POST Switches and set the COMPRESS E XPAND Control to the 1 0 Position Do not switch the 128 while recording 3 With your tape machine in the Record Ready Pause mode s...

Page 6: ...e i e PHONO TUNER or AUX and the TAPE MONITOR Switch to TAPE 2 Press the 128 s DISC BYP and POST Switches and set the ABOVE THRESHOLD LINEAR Switch to the LINEAR position IN 3 Set the COMPRESS EXPAND...

Page 7: ...primary reason for this lack of excitement and realism is the dynamic range limitations in the recording and broadcast mediums Dynamic Range and Why It Is Important Dynamic range can be defined as th...

Page 8: ...ts or you can capture all of the widest range program material on your conven tional cassette or reel to reel tape recorder using dbx II tape noise reduction dbx Il Tape Noise Reduction dbx 11 tape no...

Page 9: ...ls of background music quieter passages must be kept loud enough to be heard yet loud passages must not be too loud Similarly if you are recording music for play back in your automobile or any other h...

Page 10: ...ded disc since the encoded disc already has an extremely wide dynamic range To avoid over expansion always press the PRE button and set the COMPRESS EXPAND control to the 1 0 12 o clock position when...

Page 11: ...s not help check to make sure all audio cables are prop erly installed and that there are no broken conductors in any cable Also try cleaning the connectors on your cables since hum and radio station...

Page 12: ...he flattest frequency response Tonal adjustments can be made when playing back the tape Where to Connect Your Tape Recorder Connect the 128 s RECORD OUTPUTS to the RECORD INPUTS or LINE INPUTS of your...

Page 13: ...the 128 can be installed in the tape monitor loop and the graphic equalizer installed between the preamp output and the power amplifier input Figure 6 Equalized Speaker Systems If you have an equaliz...

Page 14: ...Decoder Etc Special signal processing follows the dbx encode decode process PREAMP TAPE a t R L Rp SPEAKER R L R L a G EQUALIZER oc cS x x uerTTO TQ FO 70 FO j RIGHT O eo e 9 ge TO TARE RECORGER EROM...

Page 15: ...ape recorder to extreme high or low settings to make the VU meters read in their normal range then adjust the REC LEVEL MATCH control as follows Place your machine in RECORD READY mode PAUSE with the...

Page 16: ...control Dubbing Copying an Encoded Disc onto a Tape in Encoded Form To dub a dbx encoded disc onto a tape and retain the dbx encoding 1 Set the 128 s front panel switches and controls as shown THRESH...

Page 17: ...pproximately the same setting used for normal recording Then adjust the 128 s PLAY LEVEL MATCH for maximum tape recorder OVU readings about 3 for cassette recorders 4 Play the disc and record normally...

Page 18: ...chine to refer to the tape machine with the program to be copied We use the term slave machine to refer to the tape machine which is to record the program 17 differences in dbx professional systems an...

Page 19: ...similar copying provisions connegt your system as shown in Figure 10 3 If your preamp or receiver has only one tape monitor loop there are two ways to make a non encoded copy Machine A Either disconne...

Page 20: ...dbx Encoded Master withoina Preamplstiers dbx encoded master blank tape machine in PLAY mode machine in REC mode dbx encoded master machine in PLAY mode blank tape machine in REC mode Y cable adapter...

Page 21: ...rding is a function of the recorded signal level as well as bias level In order to minimize tape modulation noise it is important that the tape machine be properly biased for the particular tape used...

Page 22: ...M Z ie i 9 Be nia brung ehage Dp pu fhe i Y How to Use the Expander Alone Without dbx 11 Tape 21 Noise Reduction Linear Expansion 1 Set the 128 s front panel switches and controls as shown f t Om 8 Ch...

Page 23: ...ontrol the amount of expansion while listening to the program through the 128 s expander section Set the LEVEL control to a point where the BELOW THRESHOLD and ABOVE THRESHOLD indicators are amber dur...

Page 24: ...ing one for the front two channels and the other for the rear two channels 2 Connect the QUAD CGNNECTORS of the two units together with a spare patch cable as per in Figure 13 3 Simultaneously feed th...

Page 25: ...d passages 3 Set the 128 s LEVEL control so the above THRESHOLD LED lights only on musical peaks or for the desired effect 7 7 Act ape l ee or dings vet ize tom rae bet glerehetetiges ne hte Piteg RE...

Page 26: ...ocessing occurs here when occurs here when the 128 s REC the 128 s PLAY button is In button is In ee ee ee aera L Fig 14 Signal Flow Diagram Compression Expansion Processing occurs after Tape Noise Re...

Page 27: ...1 compressed program encoded reduces dynamic range by half so that signal can be placed below the tape saturation tevel and above the tape noise level C 1 2 expanded program decoded restores the origi...

Page 28: ...B SPL to 100dB SPL When translated to an electrical signal by a micro phone the same program might go from 40dBm to 10d8m still a 50dB increase in program level passages and decreases the level of qui...

Page 29: ...t applications The bandpass filter in the signal path in the dbx I system is slightly more restrictive rolling off 1 dB at 30 Hz In addition the RMS detection circuitry in dbx II units is sensitive on...

Page 30: ...t noise reduction systems such as Dolby A Dolby B and A N R S which claim absolutely no audible effect have this residual noise present in the output dbx output noise is below 88 dBm By taking advanta...

Page 31: ...compander type noise reduction system some method must be used to sense the audio input level to the compressor when recording and to the expander when playing back Fig 18 6 6A This level detection c...

Page 32: ...same levels in record play and bypass modes for monitoring convenience Level matching is not essential for proper encode decode tracking Refer to pages 2 3 4 15 for level adjustment information Fig 18...

Page 33: ...g and decoding and circuitry Given a nominal level input at the dbx 128 input a sine shows that the net result of dbx processing does not change the wave signal swept across the audible spectrum this...

Page 34: ...act the effects of peak limiting described above Although the 128 33 works best with moderate expansion ratios while in the LINEAR mode HIGH EXPANSION RATIOS WOULD NORMALLY BE USED TO PROVIDE PEAK UNL...

Page 35: ...when the 128 is in its LINEAR mode every new program The linearity of the dbx system means Fig 19 Compression Expansion A Linear expansion operates over the entire dynamic spectrum of music irrespec t...

Page 36: ...1 1 5 expansion the 128 will expand a good 60 dB classical recording to about 90 dB of dynamic range Full realization of the benefit of this dynamic range requires both a hefty power amplifier and sp...

Page 37: ...E LEVEL ADJUSTMENT HARMONIC DISTORTION 0 5dB 50Hz to 15kHz 1dB 30Hz to 20kHz single sinewave record playback cycle 0 25dB 30Hz to 20kHz for complex music program 3dB at 20Hz for tape noise reduction 3...

Page 38: ...or rapidly rising signal level RELEASE RATE Follows signal envelope up to a rate of 180dB per second Attack and release times vary with the rise and decay of a musical signal Time responses optimized...

Page 39: ...t Power 20 a 5 Pr SS tt easnen cade eee V CHANNEL Usd 4 120 Vac 2S FIER SONNECTO PINDUTS SIGNAL FLOW NOTES Ge asso Foc ean ge ge ee I es idisdenert Sel 7 Pes fal v 8 DS ReG STANCES ARE EXORESSED coNtR...

Page 40: ...EL MATIM Raq al R Ld 12 eae BOK T 22M less 71 Qe R43 cs 16Vv 4 9 OAs aia pe sug A crag NLP RSo 100K CHANNEL 1 CHANNEL 2 COMP EXPAND 2 0 CAL rn CRE See R67 SOK R66 Rea SeK 1s ha ww yercow Py BELOW THAE...

Page 41: ...one 617 964 3210 or write to dbx Inc 71 Chapel Street Newton MA 02195 Attn Customer Service Department Should it become necessary to have your equipment factory serviced 1 Please repack the unit inclu...

Page 42: ...bx Inc 71 Chapel Street Newton MA 02195 Manufactured under one or more of the following U S patents 3 681 618 3 714 462 3 789 143 4 101 649 4 097 767 Other patents pending 4794 5M 600030 Printed in U...

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