audyssey set up

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http://www.avsforum.com/avs-vb/showthread.php?p=14456895#post14456895

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Απάντηση: audyssey set up

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What does room distortion sound like?
Instead of just hearing direct sound coming from each loudspeaker you also hear reflected sound. Each reflection represents a different path and arrives at your ears at a different time.

Human hearing blends direct and reflected sound into one, but the original sound has been replicated, changed by the room and added to the clean direct sound. This is called room distortion. And each listener, depending where they are sitting in the room, experiences this distortion quite differently.

At low frequencies sound is affected by large parallel surfaces. As they bounce between walls, sound waves fold back on themselves and generate standing waves. This is similar to tying a long string to a nail in the wall and then rapidly moving the other end up and down. After a while, a wave pattern forms on the string with some parts of it up (peaks) and others down (dips). A listener seated in the location of a standing wave peak will hear instruments as muddy and voices as boomy. A nearby listener seated in the location of a dip will hear instruments sounding tinny and voices thin.

At higher frequencies, sound reflects from coffee tables, shelves, and TV sets. These reflections arrive at different times and blend with the direct sound from the speakers. The result is bright, or nasal-sounding voices, and wiry string instruments. Also, sound sources are no longer distinct and clearly placed in the sound stage, but become wide and difficult to localize.


What is the source of sound distortion?
Reflections that arrive at different times are known as problems in the time domain. They degrade the listening experience by causing anomalies perceived in the frequency domain as well as in imaging and envelopment.

Some examples of what cause these reflections are large parallel surfaces, coffee tables, shelves, cabinets, TV screens, speaker locations, and furniture.


What is MultEQ?
Audyssey MultEQ is a acoustical correction technology that calibrates any audio system so that it can achieve optimum performance for every listener within a large listening area. There are two components to MultEQ:

(i) Automatic set up and (ii) Multi-listener equalization.

(i) During automatic set-up MultEQ first finds how many loudspeakers are connected in the system, then determines the loudspeaker type (satellite or subwoofer), checks the absolute polarity of each channel, and identifies the optimum crossover frequency for each loudspeaker and the subwoofer(s). After that it calculates the distance between each loudspeaker and the first microphone position in order to automatically sets the appropriate delays. Finally, it identifies any level differences among the loudspeakers and automatically sets the trims.
(ii) The multi-listener equalization process combines measurements from several locations within the listening area to create filters that address the acoustical problems arising from the interaction of sound with the environment.

How is MultEQ different from other equalization methods?
There are two fundamental differences from every other method available in AV receivers today. The first is that MultEQ is not based on parametric equalization. Parametric equalization relies on a few bands that are centered at certain frequencies. These bands do not provide sufficient resolution to address many room acoustical problems. Also, parametric bands tend to interact so that changes at one frequency have undesirable results at nearby frequencies. Moreover, parametric equalization methods use a particular type of digital filter called Infinite Impulse Response (IIR) that only attempts to correct the magnitude response in the frequency domain. These filters can cause unwanted effects, such as ringing or smearing, in the time domain particularly as the bands get narrower. MultEQ uses Finite Impulse Response (FIR) filters for equalization that use several hundred coefficients to achieve much higher resolution in the frequency domain than parametric bands. Furthermore, by their nature, FIR filters simulatneously provide correction in the frequency and time domains. FIR filters had been considered to require too many computational resources. But Audyssey solved this problem by using a special frequency scale that allocates more power to the lower frequencies where it is needed the most.

The second major difference is that MultEQ combines multiple measurements to create equalization filters that better represent the acoustical problems in the room. Most other methods only perform a single point measurement and this can result in making other locations in the room sound worse than before equalization. There are some methods that use spatial averaging to combine multiple room measurements. Although this is a step above single-point correction, it does not provide optimum correction when discussing spatial averaging. For example, it is common to find a peak at a certain frequency in one location and a dip at the same frequency at another nearby location. The averaging methods will add the peak and the dip and this will result in an apparent flat response at that frequency, thus causing the equalization filter to take no action. MultEQ uses a clustering method to combine measurements so that acoustical problems are better represented, thus allowing the equalization filter to perform the appropriate correction at each location.


Does MultEQ eliminate the need for acoustic treatment?
No. Although MultEQ will improve sound significantly in untreated rooms, a properly treated room calibrated with MultEQ can achieve stunning results throughout the listening area.


How many listening locations can be measured?
The equalization performance increases with the number of measurements. Audyssey recommends a minimum of 4 with most rooms performing best with 6 measurements. The maximum number of measurements is limited by the available memory in the receiver or controller and in some products can go up to 8.


What are the recommended measurement positions?
The first microphone position must always be in the center of the listening area. Then we recommend moving the mic about two feet to the left of that first position for measurement two and two to the right of the original spot for measurement three.

If you are running MultEQ or MultEQ XT you should use all six or eight measurements available. The next three should be taken about two feet in front of the first three. The final two measurements (if available) should be about one foot to the left and right of the first central measurement and about one foot forward to form a triangle.

You should avoid taking measurements that are too far off to the side and outside the front Left and Right loudspeakers even if there are seats there. These measurements will suffer from a drop in high frequencies and can cause the room correction filters to compensate for that unnecessarily.

Also avoid taking measurements too close to the back wall even if the only listening seats are up against the wall. Move the mic at least one foot from the back wall to avoid the bass build-up that happens there.


Why does Audyssey set my speakers to Large (or Small) when I know they are not?
MultEQ does not set the speakers to Large or Small. This is a decision made by each individual AVR manufacturer and each uses a different speaker roll-off frequency to make this decision. Audyssey recommends the decision should be made using 40 Hz as the roll- off frequency. That is to say, if a speaker is found to roll-off below 40 Hz it should be called Large and all other speakers should be called Small.

If your AVR manufacturer sets your speakers to Large then all content below the crossover frequency is lost as it is not redirected to the subwoofer. Audyssey recommends changing the speaker setting to Small manually after the calibration is finished.


Does MultEQ consider any of the settings in the receiver before running the calibration?
No, all internal settings are ignored during calibration. This includes crossover points, channel levels, delays, tone controls and master volume.


Is there a danger of overdriving the loudspeakers by using MultEQ?
No, MultEQ filters are calculated by taking into account the capability of the loudspeaker and the overall gain structure of the system. Limits in correction are imposed at each frequency to prevent the loudspeakers from being overdriven.


How can the performance of MultEQ be measured?
Proper frequency response measurement requires the right equipment. This includes a calibrated 1/4" microphone and software that can perform averaging over time and space. Unfortunately, many of the programs available on the internet or elsewhere do not perform room measurements correctly and this can give rise to misleading results. For example, many only allow a single microphone position and do not perform time averaging. The simple solution of a CD with sinusoidal tones and a sound pressure level meter is also inappropriate for measuring room responses because of the sensitivity of sinusoids to standing waves. For recommendations on proper room measurement techniques and software please contact Audyssey Laboratories.


What is a target curve?
Once the room measurements are completed, MultEQ calculates a filter for each loudspeaker channel including the subwoofer. The role of these filters is to achieve a particular frequency response within the entire listening area for each loudspeaker. This curve is determined based on several acoustical and program material considerations and is called a "target" or "calibration" curve.


What target curves does MultEQ use?
Contrary to popular belief, a target curve that is flat from 20 Hz to 20 kHz is not always the one that will produce the correct sound. There are several reasons for this including the fact that loudspeakers are much more directional at high frequencies than they are at low frequencies. This means that the balance of direct and room sound is very different at the high and low ends of the frequency spectrum.

The Audyssey target curve setting makes the appropriate correction at high frequencies to alleviate this problem. A slight roll-off is introduced that restores the balance between direct and reflected sound.

The Flat setting uses the MultEQ filters in the same way as the Audyssey curve, but it does not apply a high frequency roll-off. This setting is appropriate for very small or highly treated rooms in which the listener is seated quite close to the loudspeakers. It is also recommended for all rooms when the receiver is in THX processing mode. This allows THX re-equalization to operate exactly as it was intended.

The Front setting uses the MultEQ filters that were calculated for the entire listening area, but it does not apply any filtering to the front left and right loudspeakers. The average measured response from the front left and right loudspeakers is used as the target curve for the remaining loudspeakers in the system. The subwoofer in this case is equalized to flat as is the case for all the settings described above.

In some products, there is a Manual setting. This is a traditional parametric equalizer that does not use the MultEQ filters or measurement process at all.


Why does MultEQ correct beyond 300 Hz?
There is a belief that room correction should only be applied to frequencies below 300 Hz or so because that is the frequency range in which most of the room problems occur. This belief is based on an inherent assumption that a properly designed loudspeaker will perform as desired at higher frequencies and thus require no correction. This is not at all contradictory to MultEQ. If the loudspeaker is in fact properly designed then no correction will be applied to it. One simple fact that the proponents of this theory seem to overlook is that even the best designed loudspeakers will suffer from artifacts at high frequencies produced by reflections from nearby flat surfaces such as plasma screens or cabinets. MultEQ performs this kind of correction when it is needed to allow the loudspeaker to achieve the performance it was designed to have.


My speakers are wired correctly, why does MultEQ give a "Phase" error?
MultEQ detects absolute phase for each loudspeaker. Some loudspeakers are designed with intentional phase reversals in the drivers in order to address crossover problems. MultEQ will detect that and report an error. The best course of action is to simply check the wiring and press "Skip" if it is correct. MultEQ simply reports a possible wiring reversal, it does not automatically switch the phase.


Is the microphone calibrated?
Yes, the microphone is calibrated to a 1/4" industry-standard measurement microphone. The correction is applied to the measurements as they are being taken. It is important to use ONLY the designated microphone that comes with the product as the calibration curve built-in to the product is specific to that microphone. It is also critical to point the microphone upwards and to place it at ear height. Any other microphone will have different characteristics and thus will not produce the right results.


What is the proper way to point the microphone?
The microphones used in MultEQ are all calibrated for grazing incidence and should point to the ceiling. Standing near or behind the microphone or holding it in your hand will introduce serious measurement problems including reflections and low frequency noise that will affect the performance of the filters.


What happens to the MultEQ settings when the parameters are changed?
MultEQ corrects for room acoustical problems. Changes in the tone controls do not change the filter performance. They do change the tonal balance based on the preferences of the customer. The benefit of MultEQ is that it allows a customer (or installer) tone control setting to work on all program material in a much more predictable way than it would on an uncalibrated system.

Does MultEQ compensate for loudspeakers placed behind a projection screen?
If the calibration is performed with the screen in place, MultEQ will automatically create filters for behind-the-screen loudspeakers that compensate for the screen loss.


How well does MultEQ work at low frequencies?
This is one of the unique strengths of MultEQ. Room correction methods based on parametric equalization do not have enough bands or processing power to apply correction in the bass frequency range. MultEQ uses a unique implementation of FIR filters that achieves very good resolution at frequencies below those that standard FIR filters can reach. The resolution of the MultEQ filters varies with frequency and this allocates more of the filter correction power where it is needed the most: in the lower frequencies.


My subwoofer is physically closer than the distance reported by MultEQ. Why?
Many powered subwoofers do not provide the capability to defeat the built-in low-pass filter. These filters, by their nature, introduce additional delay in the signal and MultEQ finds that and reports it. The optimum solution is to turn the filters off (often called "LFE mode" in subwoofers). If that is not possible, set the low pass frequency to the highest possible setting and leave the distance reported as is. MultEQ will compensate for the added delay and time align the subwoofer to the satellite channels so that the optimum blend is achieved.

 

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Απάντηση: audyssey set up

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