Aphex Systems 320A owner manual Appendix F, Confusion, Where The Problem Comes From, PPM Standard

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320A

Appendix F

Compellor

Appendix F

Digital–vs–Analog; Peak–vs–RMS

How To Deal With The Confusion

By Donn Werrbach • 10/03/03

The Confusion

The matter of audio level measurements and specifications can be very confusing at times. That is because some specs relate to peak measurements and some to average or RMS measurements. There is no one standard in use throughout the industry.

Where The Problem Comes From

Any sound’s tonality and intelligence is conveyed by the details of specific frequency com- ponents, and those components’ phase and amplitude relationship. Sounds contain not only harmonics in varying amounts, but also may contain unrelated frequency components. These all add up to create complex and varying audio waveforms.

If all sound were nothing but pure simple sine waves (the most fundamental wave of nature), the measurement of sound would be very simple. Measurements, whether peak weighted or average weighted, would almost come out the same. A sine wave’s peak level is only 3dB higher than it’s average level, and what’s more important, the ratio of peak to average, also called the “crest factor”, is always the same no matter what the level is. Both peak and aver- age level meters could be calibrated in the same relative units (like VU) and would read the same.

However, since sound waves are complex, their peak to average ratio varies depending on the sound characteristics, and that ratio can vary from 3dB to as much as 15dB. So, in the real world, peak and average meters will disagree by as much as 15dB. The ear hears loudness based on the power level contained in a sound wave. The power level is proportional to the average signal level, so averaging meters will respond to level more like our hearing. Peak measurement of audio cannot infer the volume level except with pure test tones because the crest factor of program audio is large and variable, kicking the peak meter well above the average measurement.

The problem is that we find both kinds of meters in use and they cannot be easily recon- ciled.

Dueling Standards

The PPM Standard

Throughout Europe, and its sphere of influence in the world, professional analog standards have been based upon some form of peak audio measurement. One of the most popular standards is the German DIN Peak Program Meter (PPM). These are found on recording consoles, program line meters, tape recorders, and everywhere else. These meters have a 10 millisecond peak integration time and several seconds of fallback time. As a result, not all transient peaks are captured by the meter, but the readings tend to ride atop the typical peak level, totally disregarding the average level.

An advantage of this method is that audio electronics need not be built with very much head-

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Contents 320A Safety Declarations Fast Finderi320A Contents Page Quick Start Quick StartWhat Is a Compellor? What Does It Do?How Does It Work? Bit Of Compellor HistoryIntroduction Page Unpacking Damage & ClaimsMains Voltage Selection And Fuse Power Cord Safety ConsiderationsMounting In a Rack Proper VentilationInstallation Remote ConnectorReference Level Setting Input ConnectionsSummary Specications Ratio Introduction RecordingMixing MasteringVideo Post-Production Live ConcertsBroadcast Radio Pre-processing Broadcast STL/ Phone Line Driver Television Broadcasting and Cable SystemsVideo and Audio Tape Duplication Voice ProcessingHard Disk Recording Signal Flow Processing FunctionsLeveling Function Compressor Function DRCDVG Silence GateStereo Enhance Stereo LinkingMeter Selections LimiterProcess Switch Output ControlInput/Output Operating LevelsGain Reduction Metering Limited Warranty To Obtain ServiceAppendices Appendix B 320A Appendix C Proper Wiring Techniques Appendix CAppendix D Appendix D Part 1 Balanced OUT to BalancedImpedance Balanced Outputs Part 5 Y Insert Cables Appendix E Appendix E Compellor to the RescueWhere The Problem Comes From Appendix FConfusion PPM StandardAppendix F VU StandardWhere The Compellor Fits Death of a Perfectly Good VU MeterBirth of dBFS DAT TragedyIdeal Audio Package Analog/Digital Level DiscrepancyWhat, Me Worry?

320A specifications

The Aphex Systems 320A is a dynamic processor designed to enhance the quality of audio recordings in professional settings. Known for its exceptional performance and versatility, the 320A offers a unique combination of compression, limiting, and expansion functionalities. This unit is an essential tool for sound engineers and producers looking to achieve polished sound.

One of the standout features of the 320A is its dual channel processing capability. This allows users to apply dynamic processing to two separate audio signals simultaneously, making it ideal for stereo or dual mono setups. The 320A offers a range of controls, including threshold, ratio, attack, release, and gain, allowing precise adjustments to be made according to the needs of any project.

The 320A utilizes Aphex's proprietary Intelligent Clipping technology, which helps to prevent distortion at high signal levels. This feature is particularly beneficial when working with dynamic sources like vocals and percussive instruments. Intelligent Clipping ensures that the audio remains smooth and clear, even when processed aggressively.

In terms of connectivity, the Aphex 320A is equipped with balanced XLR and TRS inputs and outputs, ensuring compatibility with various audio sources and devices. The unit supports both line-level and mic-level signals, providing flexibility for different recording scenarios. Additionally, its low noise operation ensures that the final output retains pristine audio quality.

Another significant characteristic of the 320A is its user-friendly interface. The front panel features easy-to-read meters and clearly defined controls, making it straightforward for users to monitor the audio levels and adjust settings in real-time.

The 320A also includes a sidechain capability, allowing users to trigger compression or expansion from an external source. This feature is useful for achieving effects like ducking or creating rhythmic dynamics in a mix.

In summary, the Aphex Systems 320A is a feature-packed dynamic processor that serves as an invaluable tool for audio professionals. With its dual channel processing, Intelligent Clipping technology, flexible connectivity options, and user-friendly design, the 320A stands out in the realm of audio processing equipment, delivering high-quality performance for a variety of recording and mixing applications.
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