Appendix F

room above the maximum PPM indication. By controlling the audio levels to maintain good PPM readings, there can be no possibility of the electronics clipping the audio. The disad- vantage is that to maintain a good average volume level, it takes very clever people riding the gain who can accurately guess at the crest factor of all the sounds. The BBC of the U.K. has actually created standards on where to allow music, voices, and commercials to peak on their own version of a PPM. It just seems so ridiculous when you consider they could all just adopt the American VU standard.

The VU Standard

Throughout the United States and its sphere of influence in the world is traditionally found the VU meter as specified by the ASA (American Standards Association, now extinct). The name VU comes from “Volume Units”. It is the intent of VU meters to indicate the audio level as we hear it. It does not indicate the peak levels of the audio.

In VU meter practice, audio electronics must be designed to have sufficient peak headroom to allow safe passage of all unseen audio peaks. To allow this, at least 20dB of headroom above the 0VU reference level is designed into professional equipment. However, the advantage is that monitoring and controlling levels by VU indications yields pleasing consistency of sound levels without any guessing about the crest factor.

Low Crest Factor 0VU Sine Wave

Peaks At -20dB Digital, +4dBu Analog

Shaded Area =

Average Level

dB Full Scale

-20 -27 8 -27 -20

-4

Both Meters

Show 0VU

 

Sine Wave

 

 

 

 

 

 

Synth

 

 

 

 

 

7

5

3

1

0

1

+

 

 

 

7

5

3

1

0

1

+

 

 

10

 

 

 

 

10

 

 

 

20

 

 

 

 

 

 

2

3

20

 

 

 

 

 

 

2

3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VU

 

 

 

 

 

 

 

 

VU

 

 

 

 

dBFS

DIN PPM

dBFS

DIN PPM

0

+5

0

+5

-3

 

-3

 

-6

0

-6

0

-9

 

-9

 

-12

-5

-12

-5

-15

 

-15

 

-18

-10

-18

-10

-21

 

-21

 

-24

 

-24

 

-27

-20

-27

-20

 

 

-30

 

-30

 

-33

-30

-33

-30

High Crest Factor 0VU Synth Waveform Peaks At -4dBFS Digital, +20dBu Analog

-36

 

-40

 

-36

 

-40

 

 

 

 

 

 

 

 

-39

 

-50

 

-39

 

-50

 

 

 

Peak Meters

Very Different for Same Loudness

Figure F-1, Sine Wave and Complex Waveform of the Same Sound Level Compared on VU

and Peak Meters Demonstrating the Peak and Average Metering Differences

Page 37

Page 36 Page 38
Page 37
Image 37
Aphex Systems 320A owner manual Appendix F, VU Standard
Page 36 Page 38

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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