What is Audyssey Dynamic EQ?
Audyssey Dynamic EQ is the first loudness correction technology to solve the problem of deteriorating sound quality as volume is decreased by taking into account human perception and room acoustics.
Why is loudness correction needed?
Film composers, musicians, and audio engineers create the mixes of your favorite movies and music at reference levels much louder than typical home listening levels. At a lower playback volume, voices change, bass disappears, and the surround soundstage becomes less enveloping. Now, Dynamic EQ lets you enjoy the original rich sound at any volume.
How does Dynamic EQ Work?
Audyssey Dynamic EQ selects the correct frequency response and surround volume levels moment-by-moment. The result is something never before possible—bass response, octave-to-octave balance and surround impression that remain as they should be despite changes in volume. This is the first technology to carefully combine information from incoming source levels with actual output sound levels in the room, a pre-requisite for delivering a loudness correction solution.
How does Dynamic EQ work with MultEQ?
Audyssey Dynamic EQ is uniquely designed to work in conjunction with our award-winning room correction technology, Audyssey MultEQ. Before loudness correction can be implemented, the room must be corrected for both time and frequency domain problems. MultEQ effectively removes the distortions caused by the acoustics of your room and the unique way your system interacts with it. Dynamic EQ then determines the proper loudness compensation based on the sound pressure level measurements MultEQ provides. Audyssey Dynamic EQ working in tandem with Audyssey MultEQ provides the right listening conditions for every listener at any volume level.
Dynamic EQ with MultEQ: The frequency response stays the same as volume is decreased.
Dynamic EQ turned off: Bass response is diminished and voices changes as volume is decreased
Dynamic EQ On with MultEQ: The frequency response stays the same as volume is decreased.
Loudness systems without MultEQ: Playback system is not calibrated for the room resulting in incorrect adjustment
Hasn't loudness correction been around for years?
Experiments by researchers at Bell Labs in the early 1930s showed that humans don't perceive low bass and high treble frequencies as well at lower volumes. Audio manufacturers tried to compensate for this by adding a loudness correction option to their products, however this could not be correctly implemented without advanced DSP technology. Loudness compensation controls had a tendency to sound too boomy and artificial in the bass and treble ranges. Loudness correction was dismissed as inadequate and by 1980 most manufacturers had
removed loudness controls from their products.
Tomlinson Holman, inventor of THX, currently Audyssey Chief Science Officer, and USC School of Cinematic Arts Professor, investigated these problems in his classic 1977 paper, "Loudness Compensation: Use and Abuse." This paper, published in the peer-reviewed Journal of the Audio Engineering Society, explained the fundamental problems preventing loudness from working correctly in audio systems of the time:
- Existing loudness controls were based on the wrong curves. Most loudness controls were based on data collected at Bell Labs by Fletcher and Munson in the 1930s. While these curves characterized the effect, the measurements themselves were imprecise, due to the primitive equipment that was used at that time.
- Existing loudness controls were based on the Fletcher-Munson curve themselves. In order to hear content played back at a different volume than the original, loudness compensation controls should have been based on the difference between the curves of the reference level and the playback level.
- No input level calibration was available. There was no way to know the original mix level of the program material. Thus, there was no starting point to find the difference between the original level and the playback level.
- No output level calibration was available. Varying electrical gain after the volume control, speaker sensitivity, and room acoustics made it impossible to determine the exact output level. These factors all conspired to make a particular volume control setting to be reproduced with very wide variations.
- Loudness controls were not dynamic. For example, an orchestra typically plays at 100 dB SPL on peaks and at 50 dB SPL during soft passages. When the volume is turned down by 20 dB for home listening, the peaks and soft passages require different loudness correction. More compensation is required when the starting level is low and attenuated than when high and attenuated. This lack of content-based dynamic control also added to the boomy bass of earlier loudness systems.
How does Dynamic EQ address these problems?
After years of research, the Audyssey team determined Dynamic EQ could now be a viable product:
- New research has produced more accurate data. The last 30 years have produced more refined data from Fletcher and Munson's original findings. Thousands of listeners participated in experiments around the world to define today's more accurate standardized curves. Audyssey Dynamic EQ has customized this data to the home theater environment, with a special emphasis on accurate multi-channel loudness compensation.
- It is now possible to calculate difference curves. Audyssey developed proprietary methods for the real-time calculation of differences between reference level and playback level curves.
- Input level calibration is now available. Movie program material is now mixed at a standard level. Music and television programs are also starting to adopt a standard. Recorded program levels can now be traced back to the acoustical levels of the original mix. Audyssey uses this information to apply the proper loudness correction.
- Audyssey performs output calibration. In receivers, output calibration is achieved with MultEQ and an Audyssey-calibrated microphone. In packaged systems, loudness calibrations are performed in advance, because everything is known in the signal chain.
- Audyssey Dynamic EQ is the first truly dynamic loudness control. Dynamic EQ evaluates the content in real time, updating the loudness control curves so that both soft and loud passages receive the proper treatment.
These breakthroughs were possible because of Tom Holman's original findings, advances in DSP technology, and present-day research on the principles of loudness correction by the Audyssey team.
How is Dynamic EQ different from other loudness methods?
Other loudness correction methods have been proposed, but Audyssey Dynamic EQ is the first to address all of the five major problems required for proper loudness correction.
- They have no method of room measurement. Other loudness controls do not have a method for measuring the actual playback volume in the room your system is set up in. Audyssey MultEQ first measures playback levels, then provides this information to Dynamic EQ for proper loudness correction.
- They have no method of room equalization. Variations in the response of a room can be as large as 10 dB or more at some frequencies. Without proper equalization, the effectiveness of loudness correction will vary immensely from seat to seat.
- They have no real-time analysis of audio content. Film and music pieces are typically made at reference volumes much louder than typical listening volumes. At reference level, loud sounds can be near 100 dB SPL, while soft sounds can be much softer, near 50 dB SPL. If a consumer listens at softer levels such as 20 dB down, loud sounds will need less loudness correction than softer sounds. This must be analyzed continuously to ensure the correct octave-to-octave balance is sustained as the content is playing.