Page 1: ...INSTRUCTION MANUAL dbx ll NOISE REDUCTION SYSTEM 124 dbx ll NOISE REDUCTION syYSTEM 7 CHAI ANNELLS 1 3 e...
Page 2: ...THE MOSTOUTOFdbxNOISEREDUCTION C HOW dbx TAPE NOISE REDUCTION WORKS 28 SYSTEM PERFORMANCE 32 TECHNICAL DETAILS OF dbxPROCESSING SPECIFICATIONS OOOO DISCUSSION OF SPECIFICATIONS C t CCLTOCOOO dbx PRODU...
Page 3: ...FUNCTIONAL CALLOUTS NWO SS ma S A s ws A la y Fig 1 Model 122 and Model 124 Front Panels Descriptions on next page...
Page 4: ...des D Play Level Match This control allows you to adjust the 122 s output level to your preamplifier Like the RECORD LEVEL MATCH control this adjustment is not critical and does not affect the lineari...
Page 5: ...LAY RECORD LEVEL MATCH INPUTS OUTPUTS INPUTS ouTPuTS a Y MODEL 124 _ aay Dy YW I2 KOW DS TO TAPE RECORDER AURILIARY OR LINE INPUT TO PREAMP TAPE GR aVINA Fig 2 Model 122 and Model 124 Rear Panels Desc...
Page 6: ...ese outputs to your preamplifier s TAPE INPUTS Play Inputs of the tape monitor loop These cables previously came from your tape recorder s LINE or AUX Play OUTPUTS Use only the 2 and 4 PLAY OUTPUTS fo...
Page 7: ...8 A S Fig 3 Connecting the dbx 122 in a Tape Monitor Loop 2 a E 3 a 4 w x a iow io w x w a a BACK FRONT Cs ris rl Vi aoe Co mal ee ES A ve Ore t AN A oe p cl Am R Z a Fig 4 Connecting the dbx 124 in a...
Page 8: ...mplifier having Two Tape Monitor Loops rs aif Fig 6 Connection of the 124 with Two Tape Machines and a To simultaneously record and monitor on machine A set the 124 s channel 1 3 switches to REC and c...
Page 9: ...bx processing permits recordings to be made at levels that avoid much of the distortion which normally occurs in tape recording As a result dbx equipment not only reduces noise it can vastly improve t...
Page 10: ...sa even though all dbx tape noise reduction systems offer the same 30dB of tape noise reduction and 10dB headroom improvement The incompatibility is due to signal processing differences as described o...
Page 11: ...that does not help check to make sure all audio cables are properly installed and that there are not broken conductors in any cable Hum and radio station pickup are sometimes caused by microscopic di...
Page 12: ...tonal adjustments can be made later during playback of the dbx encoded tape Where to Connect Your Tape Recorder 11 Connect the dbx s RECORD OUTPUTS to the RECORD INPUTS or LINE INPUTS of your tape re...
Page 13: ...ro Voice Interface series then the dbx unit can be connected in the speaker equalizer s tape monitor loop and the equalizer should be installed in the preamp s tape monitor loop Figure 9 NOTE Never co...
Page 14: ...PNA i Sop Fig 9 Connecting the dbx Unit with an Equalized Speaker System dbx processing is done inside the tape monitor loop of the speaker equalizer which itself is in the tape monitor loop of the pr...
Page 15: ...d as shown in Figure 10 This setup allows material to be recorded in encoded form and monitored off the tape in decoded form at the same time Arbitrarily channels 1 3 are assigned for recording and ch...
Page 16: ...odel 122 has a PLAY LEVEL MATCH control on its front panel a knob that adjusts both tape and disc playback level at the same time The Model 124 has a TAPE PLAY LEVEL MATCH control screwdriver adjustab...
Page 17: ...r you are playing conven tional sources dbx in Bypass mode or dbx encoded sources dbx in Play mode Adjusting the 124 s Disc Play Level Match Control 1 Set the 124 s front panel switches as shown below...
Page 18: ...le from your speaker system use as much physical separation as possible a foam mat or any workable acoustic isolation technique If dirt or static electricity build up on dbx discs they can create nois...
Page 19: ...ocessing significantly lower record levels are often required to eliminate tape saturation particularly in cassette recording Experiment during initial setup to find the appro priate levels These or e...
Page 20: ...124 e 006 06 ae d 6 O60 66 ta 2 Set your preamplifier as follows TAPE MONITOR switch to TAPE and INPUT SELECTOR switch to PHONO 3 Set your tape recorder to Record and record normally 4 The tape copy...
Page 21: ...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 have no more audible noise than the original master tape NOTE...
Page 22: ...oded copy 1 Either a disconnect the dbx PLAY OUTPUTS from the preamp s Tape Monitor Inputs and connect the cables instead to the slave machine s Record Inputs Figure 15A or b simultaneously connect th...
Page 23: ...A Making a Non Encoded Copy from a dbx Encoded Master without the Benefit of Two Tape Monitor Loops without any preamp LEFT tO MASTER Fig 15B Making a Non Encoded Copy from a dbx Encoded Master withou...
Page 24: ...124 will both encode and decode simultaneous ly and thus allows stereo monitoring or real time source tape comparison when used with three head tape machines Overdubbing and sound on sound also becom...
Page 25: ...and monitor the balance at the mixer s headphone output or at your tape recorder headphone output If necessary add an additional headphone amplifier as shown 6 The encoded output from dbx channels 1 3...
Page 26: ...switches or adjustments experiment to find the settings that yield the lowest tape modulation noise and the best frequency response with dbx encoding and decoding Proper head alignment is also importa...
Page 27: ...preamplifiers the cut off frequency may be higher than necessary If unexplained playback level deviations occur after copying a conventional phonograph disc onto a tape using dbx II tape noise reduct...
Page 28: ...LEFT tO c x ia nee A oman RIGHT O e Z z A Fig 18 Using the dbx 118 in conjunction with a dbx 122 or 124 Tape Noise Reduction System The 118 is illustrated but any dbx dynamic range enhancer is suitab...
Page 29: ...io which is typical of many good hi fi and semi pro tape machines there is no way the original program dynamics can be captured on tape peaks will be lost due to saturation or quiet passages will be l...
Page 30: ...E 50 60 80 80 NOISE FLOOR OF dbx UNIT 88 100 Fig 19 How the dbx System Works C 1 2 expanded program decoded restores the original A Typical program of wide dynamic range about 100dB dynamic range 100d...
Page 31: ...g or other coloration of the sound Critical level matching is not needed because the dbx system encodes and decodes accurately despite differences in record and playback levels The Two dbx Systems dbx...
Page 32: ...se reduction as well as tape recording The dbx II system is also equipped with a TAPE DISC switch that introduces a further low end roll off 3dB 30Hz in DISC mode This has been provided to permit deco...
Page 33: ...idence that 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 88dBm By takin...
Page 34: ...hniques employed by a given compander type noise reduction system some method must be used to sense the audio input level to the com pressor when recording and to the expander when play ing back Figur...
Page 35: ...s Filter The same filter is used for encoding and decoding and rolls off 3dB at 27Hz and 10kHz The filter affects only the rms level detection preventing expansion and compression circuits from reacti...
Page 36: ...de and Decode Response output will do Note that the overall encode and decode response This is the combined effect of encoding and decoding The curve curve H is essentially flat a combination of the P...
Page 37: ...al is recorded What might be heard for example is a low organ or bass guitar note that is accom panied by a rushing hissing sound as the note dies so does the noise dbx applies pre emphasis and de emp...
Page 38: ...Hz single sine wave encode decode cycle 40 25dB 30Hz to 20kHz for complex music program 3dB at 20Hz for tape noise reduction 3dB at 27kHz for disc decode mode 2nd Harmonic less than or equal to 0 1 en...
Page 39: ...nit itself is capable of 30Hz to 20kHz response 1dB and is within 0 5dB between 50Hz and 15kHz Encode decode harmonic distortion consists primarily of low frequency third harmonics and is the result o...
Page 40: ...4 3210 Telex 92 2522 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 i...
Page 41: ...The SUES p od El Ore He os S NOTES LUNLESS OTHERWISE SPECITIED ARES TORS ARE EYPRESSED IN OHMS ye ake Bo kaAne nt sa2z21 238 AME NUNS AND AE AST REFERENCE 11 SIONATIONS C23 ORs Q2 H45 54 71 Pt PCR OR...
Page 42: ...s as REO ges be SOK _rs co a RECORD PLAY ov LEVEL LE vet pa cen MATCH TAAT Cts 4 RoNT PANEL FY v PEAR Panty wa REAR PANEL fret Core Pre AZ out ne e w 4 3 3 Se A 22 UF ION Sev 3 Po crn bs al TAPE 0 Ke...
Page 43: ...UT CHANNEL 2 Tear our Trecoanl 8 our 2 I i 4 CHANNEL 4 Pao Ay Ceo Bid V ae iz ce v WE3SVCp i ce ite alomresy cB wiley ms 2 Pr cre N4383 I 270 SWOT Ww nal 19084 20v ne ROWER E NOTES LUNLESS OTHERWISE S...
Page 44: ...c PLAY es LEVEL LEVEL Mie rye f MATCH MATCH fRECGRO OISE Vv v a ad FRE CORO LG Pik i Pc2 aeiss _ al can Bu 6 o ganrev peat5 TAPES 4 t AN ez ere fsear He 2700 SWIOK Ww nef escousl S9F_fra tae CHANNEL 2...
Page 45: ...factured under one or more of the following U S patents 3 681 618 dbx Inc 3 714 462 3 789 143 4 101 849 4 097 767 Other patents pending 71 Chapel Street Newton MA 02195 et 4792 5M 600071 Printed in U...
