DOCSLIB.ORG

Audio Signal Processors?

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

A Shure Educational Publication Selection and Operation of Audio and Operation Signal Processors Audio Signal Processors By Gino Sigismondi Selection Selection T ABLE OF C ONTENTS INTRODUCTION . 4 What Are Audio Signal Processors? . 4 What Types of Problems Can Benefit from Audio Processing? . 5 Feedback . 5 and Operation CHAPTER 1 of Audio Signal Processors TYPES OF AUDIO PROCESSORS . 6 1.1 Volume (Gain) Control . 6 1.2 Filters and Equalization . 6 1.3 Dynamics Processors . 11 1.4 Delay . 15 1.5 Adaptive Audio Processors . 15 CHAPTER 2 PRACTICAL APPLICATIONS FOR AUDIO SIGNAL PROCESSORS . 20 2.1 Maximizing Gain-Before-Feedback . 20 2.2 Improving Speech Intelligibility . 21 2.3 Sound System Gain Structure . 23 2.4 Digital Signal Processing . 25 REFERENCE INFORMATION . 26 Appendix 1: Sound Waves . 27 Appendix 2: Potential Acoustic Gain (PAG) and Needed Acoustic Gain (NAG) . 29 Glossary . 34 References . 34 Acknowledgements . 34 Biography . 34 Additional Shure Educational Publications . 34 3 I NTRODUCTION For any sound system, the primary goal is good sound. What, however, constitutes "good" sound? The three primary INSTRUMENT MICROPHONE AMPLIFIER of Audio Signal Processors measures of good sound are audibility, intelligibility, LOUDSPEAKER and fidelity. Many factors and Operation contribute to the quality of VOCAL MICROPHONE the sound, including the quality of the sound MIXER PROCESSOR BOUNDARY sources, the sound system, MICROPHONE and the room acoustics. The audibility of speech or music at the Figure 1-1: basic sound system furthest listener must be sufficient to achieve the desired effect: usually a comfortable listening level for system design. A basic sound system consists of four speech, and more powerful levels for certain kinds of components: music. These levels should be attainable without • Input devices (microphones, CD players, etc) distortion or feedback. Intelligibility is determined by • Mixers (to combine inputs, control levels, Selection the signal-to-noise ratio and direct-to-reverberant ratio and provide preamplification, if necessary) at the listener’s ear. The "signal" is the desired sound • Amplifiers source (speech, musical instruments, etc.), while the • Output devices (loudspeakers) "noise" is ambient sound in the room as well as electrical noise produced by the sound system. Audio signal processors are typically employed Maximum speech intelligibility requires a speech level within or just after the mixer stage, but before of at least 20 dB above the noise floor at the listener’s amplification. (See Figure 1-1.) A processor can be used ear. The direct-to-reverberant ratio is determined by the at the input stage, but since most processors are directivity of the loudspeakers and the reverberation designed to operate with line level sources this is rare. characteristics of the room. High levels of reverberation Signal processors can be analog or digital, single- or can severely degrade intelligibility by making it difficult multi-function, stand-alone devices or integrated with to distinguish the end of one word and the start of the other components in the sound system. Most signal next. Finally, fidelity of sound is primarily defined by the processors originated as stand alone devices overall frequency response of the sound arriving at the designed for a specific purpose. Over time, integration listener’s ear. The frequency range must be sufficiently of similar processors into one device became popular wide and relatively uniform in order to provide realistic (e.g. compressor/limiters). The development of audio and accurate reinforcement of speech and music. processors that operate in the digital domain allowed Every component in the signal chain contributes to for further integration, leading to multi-function digital this, and a limitation at any point will affect the fidelity signal processors (DSP) that combine seemingly of the entire system. disparate functions into a single unit. Perhaps more Other more subjective terms may be applied to good importantly, DSP devices offer these functions at a cost sound ("warmth", "punch", etc.), but these colloquialisms that is a fraction of the purchase price of several are not measurable in any meaningful way. Additionally, individual processors. if the three primary measures are not satisfied, any subjective terms take on even less importance. Speech What Types of Problems Can Benefit from Audio that is "warm" but unintelligible does the listener little good. Processing? Audio signal processors offer a variety of tools To understand the purpose of audio signal to assist in optimizing a sound system for audibility, processing, it is necessary to examine the problems intelligibility, and fidelity. While not usually essential for encountered in a typical sound system. Note that an a sound system to operate (i.e., provide high- audio processor cannot solve all the potential level sound reinforcement of low-level sources), audio problems in a sound reinforcement system. The most signal processors can be invaluable tools in sound common problems are listed on the next page: 4 Selection I NTRODUCTION Once sound energy is introduced into the acoustic space Problems: Remedies: by the loudspeaker, processing no longer has any effect Feedback Parametric Equalizer/ on the sound. Reverberation can be reduced only by Automatic Mixer/ absorptive acoustic treatment or structural modification; Feedback Reducer electronics cannot remove it. If additional acoustic treat- Poor tone quality (subjective) Graphic equalizer ment is not an option, directional loudspeakers allow the Sound source too loud Compressor/Limiter/AGC sound to be "aimed" toward the listener and away from Sound source too quiet AGC reflective surfaces. Simply raising the level of the sound Varying signal levels Compressor/Limiter/AGC from multiple sound sources system will only aggravate the problem by raising the Unwanted noise Noisegate/Downward expander reverberation level as well. Long reverberation times and Operation Unexpected transients Compressor/Limiter/No overshot severely reduce intelligibility. In audio teleconferencing ("Look-ahead") Peak Limiter systems, this results in a hollow, or "bottom-of-the-barrel" of Audio Signal Processors Comb filtering Automatic Microphone Mixer sound received by the remote site. due to open microphones Frequency response Delay FEEDBACK anomalies due to misaligned loudspeakers Poor intelligibility Parametric Equalizer/ Feedback is characterized by a sustained, Automatic Microphone Mixer ringing tone, which can vary from a low rumble to a Acoustic echoes Acoustic Echo Canceller piercing screech. Echoes and reverberation caused (in teleconferencing systems) by room acoustics, as well as ground buzz and other Distortion Compressor/Limiter extraneous noises, are not the same thing as (due to wide dynamic range) feedback, and cannot be cured in the same manner. Problems that cannot be solved by audio processing: Feedback occurs whenever the sound entering a • Echoes because of poor room acoustics microphone is reproduced by a loudspeaker, picked up • Poor sound due to excess room reverberation times by the microphone, and re-amplified again and again. • Feedback caused by operating beyond the limits of PAG The familiar howl of feedback is an oscillation that is (see Appendix 2) triggered by sound entering the microphone. The • Noise (amplifier hiss, ground buzz, etc.) due to improper system setup easiest way to (intentionally) create feedback is to point • Distortion due to improper gain structure a microphone directly into a loudspeaker. Placing the microphone too close to the loudspeaker, too far from The importance of good room acoustics cannot be the sound source, or simply turning the microphone up underestimated. In any room where sound reinforcement too loud exacerbates feedback problems. Other will be used, excess reverberation times introduce a myriad contributing factors are too many open microphones, of problems that cannot be solved by any audio processors. poor room acoustics, and uneven frequency response Reverberation time is the length of time that a sound in either the microphones or loudspeakers. persists in a room after the sound source has stopped. All The single easiest way to reduce feedback is to attempts should be made to keep unwanted sounds from move the microphone closer to the desired sound entering the microphone in the first place. The level of source. Additionally, using a directional microphone desired sound at the microphone should be at least 30 dB (cardioid, supercardioid, etc.) will slightly increase the above any ambient sound picked up by the microphone. amount of gain-before-feedback. Reducing the number Proper microphone placement (a full discussion of which is of open microphones with an automatic mixer will also beyond the scope of this publication) is also crucial. A good improve the situation. Try to keep microphones and rule of thumb: always keep microphones as close as loudspeakers as far away from each other as possible. possible to the sound source. Lastly, acoustically treat the room to cover hard, reflective surfaces such as glass, marble, and wood. Want to know more about proper microphone usage? Realize, though, that in certain rooms long reverberation Shure offers the following educational guides times may be desirable, such as a house of worship free of charge: used for acoustic music performance. • Microphone Techniques for Studio Recording If the system has been designed with careful • Microphone Techniques for
Recommended publications
  • And Passive Speakers?

    And Passive Speakers?

    To be active or not to be active – that is the question... To be active or not to be active – that is the question... 1. Active, passive – the situation 2. Active and passive loudspeaker – the basic difference 3. Passive loudspeaker 4. Active loudspeaker 5. The ADAM loudspeaker: passive option, active optimum 1. Active versus Passive – the Situation In any hifi-system, the loudspeakers are the pivotal component concerning sound quality. That is not to say that the other components do not matter. Nevertheless, it is indisputable that the loudspeaker is decisive for the sound of a hifi-system. It is – besides the acoustical properties of the listening room and the recording itself – the core of any music reproduction. The history of loudspeaker development has produced a great variety of very different systems and designs. The circuit technology of the frequency-separating filter that separates the audio signal into different frequency ranges is determining the design of a loudspeaker. In this respect we distinguish between active and passive systems. Usually, this is a topic that is often underestimated in its importance for sound quality. Active-passive is much more than just a technical negligibility: In fact, the impact of the dividing network on the overall sound of a loudspeaker is substantial. Active or passive – which system is preferable? Considering the aspects mentioned before, it may become a little more comprehensive why the very question comes up over and over again in the hifi-world. For decades it has been spooking as a debate on principles in the journals and magazines and for some time, now, in the web forums.
  • Introduction to the Digital Snake

    Introduction to the Digital Snake

    TABLE OF CONTENTS What’s an Audio Snake ........................................4 The Benefits of the Digital Snake .........................5 Digital Snake Components ..................................6 Improved Intelligibility ...........................................8 Immunity from Hums & Buzzes .............................9 Lightweight & Portable .......................................10 Low Installation Cost ...........................................11 Additional Benefits ..............................................12 Digital Snake Comparison Chart .......................14 Conclusion ...........................................................15 All rights reserved. No part of this publication may be reproduced in any form without the written permission of Roland System Solutions. All trade- marks are the property of their respective owners. Roland System Solutions © 2005 Introduction Digital is the technology of our world today. It’s all around us in the form of CDs, DVDs, MP3 players, digital cameras, and computers. Digital offers great benefits to all of us, and makes our lives easier and better. Such benefits would have been impossible using analog technology. Who would go back to the world of cassette tapes, for example, after experiencing the ease of access and clean sound quality of a CD? Until recently, analog sound systems have been the standard for sound reinforcement and PA applications. However, recent technological advances have brought the benefits of digital audio to the live sound arena. Digital audio is superior
  • Audio Interface User's Manual

    Audio Interface User's Manual

    Audio Interface User’s Manual Eurorack Synthesizer Modules 14 HP TABLE OF CONTENTS 1.INTRODUCTION 2.WARRANTY 3.INSTALLATION 4.FUNCTION OF PANEL COMPONENTS 5.SIGNALFLOW & ROUTING 6.SPECIFICATIONS 2 1. INTRODUCTION Audiophile Circuits League. -The main purpose of the ACL Audio Interface module is to interface modular synthesizer systems with professional audio recording and stage equipment. The combination of studio quality signal path, �lexible routing possibilities and a headphoneheadphones ampli�ier, with low capabledistortion, of drivingmakes theboth connection high and low between impedance these different environments effortless and sonically transparent. The ACL Audio Interface offers balanced to unbalanced and unbalanced to balanced stereo lines with level controls. The stereo signal from the auxiliary input,either alsowith with balanced level tocontrol, unbalanced, can be oroptionally unbalanced routed to balanced to and mixed line signals,together or can be muted. The headphone ampli�ier can also get its signal from one or the other line after the level control and mixing stage, or can be muted. Since the ampli�ier is AC coupled only at the input, but not at the output, there is an on-board DC protection circuit included. In case the headphone ampli�ier is driven into clipping, the protection can also be tripped. The module has a soft start function* and one overload indicator for every line. *With the soft start function, the interface switch is turned on after a while after turning on the Eurorack main unit. This function can prevent output of unexpecteddamage to the sound speaker. that another module will emit at startup, which will cause 3 2.
  • MINIDISC MANUAL V3.0E Table of Contents

    MINIDISC MANUAL V3.0E Table of Contents

    MINIDISC MANUAL V3.0E Table of Contents Introduction . 1 1. The MiniDisc System 1.1. The Features . 2 1.2. What it is and How it Works . 3 1.3. Serial Copy Management System . 8 1.4. Additional Features of the Premastered MD . 8 2. The production process of the premastered MD 2.1. MD Production . 9 2.2. MD Components . 10 3. Input components specification 3.1. Sound Carrier Specifications . 12 3.2. Additional TOC Data / Character Information . 17 3.3. Label-, Artwork- and Print Films . 19 3.4. MiniDisc Logo . 23 4. Sony DADC Austria AG 4.1. The Company . 25 5. Appendix Form Sheets Introduction T he quick random access of Compact Disc players has become a necessity for music lovers. The high quality of digital sound is now the norm. The future of personal audio must meet the above criteria and more. That’s why Sony has created the MiniDisc, a revolutionary evolution in the field of digital audio based on an advanced miniature optical disc. The MD offers consumers the quick random access, durability and high sound quality of optical media, as well as superb compactness, shock- resistant portability and recordability. In short, the MD format has been created to meet the needs of personal music entertainment in the future. Based on a dazzling array of new technologies, the MiniDisc offers a new lifestyle in personal audio enjoyment. The Features 1. The MiniDisc System 1.1. The Features With the MiniDisc, Sony has created a revolutionary optical disc. It offers all the features that music fans have been waiting for.
  • Ds101 Noise Gate for the 500 Series Rack System

    Ds101 Noise Gate for the 500 Series Rack System

    DRAWMER DS101 NOISE GATE FOR THE 500 SERIES RACK SYSTEM CONTENTS Warranty . 2 Safety Consideration . 2 Radio Frequencies Statement . 2 Chapter 1 - Introduction Introduction . 3 Installation . 4 Audio Connection . 4 Typical Connection Guide . 5 Chapter 2 - Control Description The Gate Controls . 6 The Key Filters . 8 Quick Start Guide . 9 Noise Gate Operation . .10 Chapter 3 - General Information If a fault develops. 15 Contacting Drawmer . .15 Specification. 15 Block Diagram. 16 Session Recall Sheet . 17 DRAWMER COPYRIGHT This manual is copyrighted © 2012 by Drawmer Electronics Ltd. With all rights reserved. Under copyright laws, no part of this publication may be reproduced, transmitted, stored in a retrieval system or translated into any language in any form by any means, mechanical, optical, electronic, recording, or otherwise, without the written permission of Drawmer Electronics Ltd. ONE YEAR LIMITED WARRANTY Drawmer Electronics Ltd., warrants the Drawmer DS101 Noise Gate For the USA to conform substantially to the specifications of this manual for a period of one year from the original date of purchase when used in FEDERAL COMMUNICATIONS COMMISSION RADIO accordance with the specifications detailed in this manual. In the FREQUENCY INTERFERENCE STATEMENT case of a valid warranty claim, your sole and exclusive remedy and This equipment has been tested and found to comply with the limits Drawmer’s entire liability under any theory of liability will be to, at for a Class B digital device, pursuant to Part 15 of the FCC Rules. Drawmer’s discretion, repair or replace the product without charge, These limits are designed to provide reasonable protection against or, if not possible, to refund the purchase price to you.
  • User's Manual

    User's Manual

    USER’S MANUAL G-Force GUITAR EFFECTS PROCESSOR IMPORTANT SAFETY INSTRUCTIONS The lightning flash with an arrowhead symbol The exclamation point within an equilateral triangle within an equilateral triangle, is intended to alert is intended to alert the user to the presence of the user to the presence of uninsulated "dan- important operating and maintenance (servicing) gerous voltage" within the product's enclosure that may instructions in the literature accompanying the product. be of sufficient magnitude to constitute a risk of electric shock to persons. 1 Read these instructions. Warning! 2 Keep these instructions. • To reduce the risk of fire or electrical shock, do not 3 Heed all warnings. expose this equipment to dripping or splashing and 4 Follow all instructions. ensure that no objects filled with liquids, such as vases, 5 Do not use this apparatus near water. are placed on the equipment. 6 Clean only with dry cloth. • This apparatus must be earthed. 7 Do not block any ventilation openings. Install in • Use a three wire grounding type line cord like the one accordance with the manufacturer's instructions. supplied with the product. 8 Do not install near any heat sources such • Be advised that different operating voltages require the as radiators, heat registers, stoves, or other use of different types of line cord and attachment plugs. apparatus (including amplifiers) that produce heat. • Check the voltage in your area and use the 9 Do not defeat the safety purpose of the polarized correct type. See table below: or grounding-type plug. A polarized plug has two blades with one wider than the other.
  • Low Power Asynchronous Digital Signal Processing

    Low Power Asynchronous Digital Signal Processing

    LOW POWER ASYNCHRONOUS DIGITAL SIGNAL PROCESSING A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science & Engineering October 2000 Michael John George Lewis Department of Computer Science 1 Contents Chapter 1: Introduction ....................................................................................14 Digital Signal Processing ...............................................................................15 Evolution of digital signal processors ....................................................17 Architectural features of modern DSPs .........................................................19 High performance multiplier circuits .....................................................20 Memory architecture ..............................................................................21 Data address generation .........................................................................21 Loop management ..................................................................................23 Numerical precision, overflows and rounding .......................................24 Architecture of the GSM Mobile Phone System ...........................................25 Channel equalization ..............................................................................28 Error correction and Viterbi decoding ...................................................29 Speech transcoding ................................................................................31 Half-rate and enhanced
  • Using Equalization on HF SSB

    Using Equalization on HF SSB

    Using Equalization on HF SSB Bill Leonard NØCU 4/27/2010 1 Topics: •Some Commonly Used Methods for Improving HF SSB Comms •Some key points about speech and hearing •The W2IHY 8 Band Equalizer + Noise Gate •What is it •When to use it •Where to use it •How to use it •What it can, and cannot do 4/27/2010 2 What is “communication”? •Communication Transfer of Information •What is “information transfer”? •CW •Digital comms •SSB Voice Different modes require different •Rag-chew methods to optimize information transfer •Breaking DX pile-ups •FM Voice 4/27/2010 3 What can we do to improve our ability to communicate via HF SSB? Typical communication path Processor Voice Mic EQ Xmtr Rcvr EQ Spkr Ear (Brain) .. .. Typical Why Not Here? Location 4/27/2010 4 Some Commonly Used Methods for Improving HF SSB Comms: 1. Improve received SNR: •Use higher gain antennas •Use higher peak transmitter power •Raise average transmit power (compression) •There is a limit: trade-off between distortion vs. SNR improvement •Some (W2IHY) claim that straight compression can degrade transmit SNR •I question this claim (all limiters exhibit “small signal suppression”) •Compression will increase background noise when no speech signal is present •Use of a Noise Gate should mitigate this problem •“Matched Filter” detection: •“Matching” filters means more than just reducing bandwidth arbitrarily •There is a limit: trade-off between distortion vs. SNR improvement •A 10 Hz filter won’t work very well with a 60 wpm CW signal •Reducing receiver noise figure will not help when atmospheric noise is dominant 4/27/2010 5 Some Commonly Used Methods for Improving HF SSB Comms (continued): 1.
  • Shure Professional Products Catalog Circa 1973

    Shure Professional Products Catalog Circa 1973

    MICROPHONES, COMPONENTS • CARTRtDGES • ACCESSORIES H www.SteamPoweredRadio.Com H s t-t LJ ~ E:: professbrol mk=rophones and components in octior AUDIO RICHMOND, VIRGINIA Al both convenhons. Shure M67 Microphone Mixers and ALPHA M675 Broadcast Production Masters saw strenuous duty ,n When you Q\11111 and operate the hrst 16-track professional the vaned ac1tvI1Ies of the Broadcast Audio Pool dunno recordmg studio In your entire state. you want to make sure coverage ot press contarencas and comm,nea heanngs that your sound equipment Is of the highest quality, relIabIl- 1ty, and versatility. During the Oamocrahc Convant1on. Shure SM61 Profes­ To the owners of Alpha Audio ,n Richmond. V1rglnIa. this sional Microphones were v,s,ble ,n the hands ot NBC floor means that Shure products w,11 be an mtegral pan of the reporters in the convention hall of Alpha s1ud10's electronic equipment Nearly two-thirds When the Republicans convened ,n August. special Shure Audio's microphones are Shure products Unidynes were on prominent and conhnuous display from Even though Alpha Audio has four brands of microphones their important pos,1Ion on the speaker's rostrum Shure for performers to choose from. Iha Shure rrt0del s are used SM6t's were used by floor commentators for both NBC and the most. accordmg to Nick Colleran. president of Alpha the MJlual Broadcasting Network Audio Oefagahon microphones at the Rapubhcan Convention ''Wa have two SM50's that we use on bass drums," Colleran were also Shure SM61 s with spac,al stand mountmgs And repons ''We have two SM53's tor vocals, electnc bass, behind the scenes.
  • The Digital Signal Processor Derby

    The Digital Signal Processor Derby

    SEMICONDUCTORS The newest breeds trade off speed, energy consumption, and cost to vie for The an ever bigger piece of the action Digital Signal Processor BY JENNIFER EYRE Derby Berkeley Design Technology Inc. pplications that use digital signal-processing purpose processors typically lack these specialized features and chips are flourishing, buoyed by increasing per- are not as efficient at executing DSP algorithms. formance and falling prices. Concurrently, the For any processor, the faster its clock rate or the greater the market has expanded enormously, to an esti- amount of work performed in each clock cycle, the faster it can mated US $6 billion in 2000. Vendors abound. complete DSP tasks. Higher levels of parallelism, meaning the AMany newcomers have entered the market, while established ability to perform multiple operations at the same time, have companies compete for market share by creating ever more a direct effect on a processor’s speed, assuming that its clock novel, efficient, and higher-performing architectures. The rate does not decrease commensurately. The combination of range of digital signal-processing (DSP) architectures available more parallelism and faster clock speeds has increased the is unprecedented. speed of DSP processors since their commercial introduction In addition to expanding competition among DSP proces- in the early 1980s. A high-end DSP processor available in sor vendors, a new threat is coming from general-purpose 2000 from Texas Instruments Inc., Dallas, for example, is processors with DSP enhancements. So, DSP vendors have roughly 250 times as fast as the fastest processor the company begun to adapt their architectures to stave off the outsiders.
  • E.1Ineïs' Jo Ujial

    E.1Ineïs' Jo Ujial

    THE BROADCAST ENGINEERS' JOUIRNA1. Ed. Stolzenberger, Editor Sec. 562, P. L. & R. 110.03 01st Avenue Richmond 11111 18, N. Y. U. S. POSTAGE Postmaster: If undeliverable for any reason, PAID notify sender, stating reason, on form 3547, postage for which Is guaranteed. F A GEHRES WGBF-ti11EßA New York, N. Y. 2232 E POWELL Permit No. 2961 EVANSVILI.E 14 IND 5151 E.1INEÏS' JO UJIAL k ' NABET National Counci Meeting: Detroit Oct. 4-8 Nie 4 NABET'S Position in TV: - NABET Intends to Maintain and Defend its Legal TV Jurisdiction Established Thru IO Years Practice S''e Page 5 VOL. 15, No. 9 SEPTEMBER, 1948 OFFII'IA1, PUBLICATION OF N. A. B. E. T. NAT'L ASS'N of BROADCAST ENGINEERS and TECHNICIANS www.americanradiohistory.com www.americanradiohistory.com REAR 150° tao° 150° 140° Broadcast Radio Engineers who want this SUPER-CARDIOID D specify - - - CARDIOID FRONT this because the Shure Super-Cardioid Broadcast Dy- namic Microphone has a super- cardioid pickup pattern which reduces the pickup of unwanted random noise en- ergy by 73%. It is twice as unidirectional as the cardioid. In the super-cardioid pattern, the ratio of front -to -rear pickup is 14 to 1-in the cardioid, 7 to 1. There is a wide, useful pickup angle at the front of the microphone while the rear response is down of the order of 15 db over a broad range of frequencies. Reverberation energy pickup is de- creased over two - thirds. The microphone can be placed close to the reflecting surfaces without objectionable effects if the rear side of the microphone is toward the reflecting surface.
  • Download PDF of This Issue

    Download PDF of This Issue

    build a Ital transposer TIGER .01 Introduced three years ago, our "Tiger .01" is still one of the finest amplifiers available in its power class. This amplifier introduced our 100% complementary circuit which has become a standard feature in many of the better amplifiers. This combined with an output triple produces a circuit that can honestly be rated as having less than .01% IM distortion at any level up to 60 Watts. Relatively low open loop gain and a conservative amount of negative feedback results in clean overload charac­ teristics and good TIM characteristics. Other features are volt-amp output limiting, plus three fuses and an overheat thermostat. Despite the "budget” price an output meter is standard equipment. Each channel measures 4% x 5 x 14. Four will mount in a stan­ dard width relay rack for four channel systems. SPECIFICATIONS 60 Watts—4.0 or 8.0 Ohm load Minimum RMS from 20 Hz to 20 KHz with less than .05% Total Harmonic Distortion. IM Distortion .................................................................... less than .01% Damping Factor . ...................... 50 or greater 20 Hz to20,000 Hz. Southwest Technical Products Corp. Hum and N o is e .....................................................................................-90 dB 219 W. Rhapsody, Dept. FM -# 20 7 /B Am plifier (single ch an n e l)..............................$ 1 10.0 0 PPd San Antonio, Texas 78216 # 207/B Amplifier — K it ....................................................$ 77 .50 PPd Would you believe a high quality preamp and control center for less than $75.00?? Well it's true. With a few hours work you can assemble our #198 preamp kit and have a unit equal to, or superior to products costing three, or four times this amount.