Tascam PORTASTUDIO 424 MKIII Owner's Manual

Also see for PORTASTUDIO 424 MKIII: Supplementary guide

Contents

Tascam PORTASTUDIO 424 MKIII Owner's Manual Manual pdf 43 page image

49The dbx is a wide-band compression-expansionsystem which provides a net noise reduction(broadband, not just hiss) of a little more than30 dB. In addition, the compression duringrecording permits a net gain in tape headroom ofabout 10 dB.A compression factor of 2:1 is used beforerecording; then, 1:2 expansion on reproduce.These compression and expansion factors arelinear in decibels and allow the system toproduce tape recordings with over a 90 dBdynamic range – an important feature, especiallywhen you're making live recordings. The dbxemploys RMS level sensors to eliminatecompressor-expander tracking errors due tophase shifts in the tape recorder, and providesexcellent transient tracking capabilities.To achieve a large reduction in audible tape hiss,without danger of overload or high-frequencyself-erasure on the tape, frequency pre-emphasisand de-emphasis are added to the signal andRMS level sensors.Cleaning the Pinch Roller1. Press a cotton swab that has been moistenedwith rubber cleaner to the pinch roller on theright hand side of the capstan shaft (or, on theleft hand side if REW is pressed). This willprevent the swab from becoming tangled inthe mechanism.2. Clean it until there is no visible residue comingoff onto the swab.3. Using a clean cotton swab, wipe off all theexcess rubber cleaner from the pinch roller.Make certain that there is no foreign matterremaining on either the pinch roller or thecapstan shaft.Cleaning the Capstan Shaft1. Clean the capstan shaft by lightly pressing acotton swab moistened with head cleaningfluid onto the shaft. Clean thoroughly and wipeoff excess fluid.Degaussing the Tape Path1. Hold the degausser about 1 m (3 feet) awayfrom the recorder. Turn it on, slowly move in tothe tape path. Move the degausser slowly backand forth, touching lightly all metal parts in thetape path. Slowly move it away again to atleast 1 m (3 feet) from the recorder beforeturning it off.2. To complete the cleaning and demagnetizingprocedure, press STOP. The head block willretract. Then hold STOP and press COUNTERRESET to cancel the cleaning mode.How the dbx WorksCAUTIONIf the surface of the unit gets dirty, wipe thesurface with a soft cloth or use a dilutedneutral cleaning fluid. Clean off thoroughly.Do not use thinner, benzine, or alcohol, asthey may damage the surface of the unit.SUBSONICS AND INTERFERENCEThe dbx incorporates an effective bandpass filter.This filter suppresses undesirable subsonicfrequencies to keep them from introducing errorsinto the encode or decode process. However, ifrumble from trains or trucks is picked up by yourmicrophone and fed to the dbx, modulation of theprogram material during low level passages mayoccur. This low-frequency component will notitself be passed through the recorder and so, willnot be present at reproduce for proper decoding.It this low-level decoding error is encountered,and subsonics are suspected, we suggest theaddition of a suitable high-pass filter in themicrophone line.80dBInputDynamic rangeofinput signalEncoder Tape deck Decoder OutputEncode(Compress) 40dB 40dBRecord Playback Decode(Expand) 80dB Saturationlevel+20dB+10dB +15dB+25dB+20dB0dBDynamic range of tape(65dB)–60dB–60dB–30dB–50dB–80dB Noise leveldbx encoding/decoding level diagramÁ Á ÁÁ ÁÁÁÁ