320A

Appendix E

Compellor

Appendix E: About Reference Levels

 

ANALOG SYSTEMS

Systems declaring the average reference level are very different than systems declaring the peak reference level. In the United States, most analog systems still use the VU meter and we declare the +4dBu (for example) reference level to be the average program level. Peak program levels may greatly exceed this level but sufficient headroom is allowed in the elec- tronics to safely carry any unseen peaks. In a peak declared system such as practiced in Europe, a maximum signal level is declared as the reference and a Peak Program Meter is used to observe the program levels.

In an average reference system, peak levels may exceed the reference level by as much as 20dB.

Thus, a +4dBu referenced system may see peaks as high as +24dBu. If we carefully con- trolled a mixed program to keep its sound level constant, we would see fairly consistent VU indications, but extremely variable PPM indications. Likewise, if we mixed the same program to keep the PPM indications consistent, the sound level would vary.

Since the Compellor is expressly concerned with controlling the sound level as the ear perceives it, only the average level bears relevance. This is an important concept to grasp if you are used to dealing with peak responding level meters, because you can- not see the Compellor’s benefits on peak meters.

When you set the Compellor’s REF LEVEL switch to match your system reference, an assumption is made of an average reference level.

For peak referenced systems, such as the +6dBu German system, the average program level will reside far below the reference level (typically 10 to 15dB below, or around -8dBu) but will be uncertain and variable depending on the peak factor of the particular sound.

DIGITAL SYSTEMS

Digital recording has almost universally adopted peak level metering. Digital level meters have 0dB at the top of the scale. That is defined as 0dBFS, or 0dB referred to full scale. It is impossible to have a digital signal that exceeds 0dBFS in peak value. If recording a signal that frequently peaks to 0dB, it is likely the signal is clipping since it is probable that some of the peak waveform is “going over the top”. Therefore, it is necessary to keep all signals peaking below 0dB in a digital system.

There are further constraints on peak levels in digital audio. Any type of digital audio process- ing can add peak overshoot. Digital effects like reverb or phasing add a lot of overshoot, as do bit reduction schemes such as MP3. For example. transmission codecs used for ISDN audio can easily add 6dB of overshoot. Therefore, it is wise to record and maintain digital audio streams at lower than -6dBFS maximum peak at all times.

In an attempt at dealing with this problem, the Society of Motion Picture and Television Engineers (SMPTE) has declared a standard of practice where 0VU is equal to -20dBFS. Most of the world’s audio industry has accepted this standard in principle, but it is widely mis- understood. The problem is the difference between peak and average level measurements, and how reconcile them.

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Aphex Systems 320A owner manual Appendix E
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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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