A Guide to Audyssey Auto Calibration & Other Technologies
A GUIDE TO AUDYSSEY AUTO CALIBRATION & OTHER TECHNOLOGIES
Although this guide is written for Audyssey AUTO calibration program, many of its suggestions can be used by people who are using other receivers/processors and auto calibration programs.
Audyssey is used by Creston, Denon, Integra, Marantz, NAD, Onkyo, Phase Technology, and Wisdom. It does not stand for anything with respect to audio. Audyssey is a name that is used by the founders of the company, Chris Kyriakakis (a Professor at USC) and Tomlinson Holman of THX.
Anthem: ARC = Anthem Room Correction Emotiva XMC-1: TACT = Tuned Aperture Computed Tomography Pioneer: MCACC = Multi Channel Acoustic Calibration and Control Sherwood: Room Acoustic Calibration with EQ Sherwood Newcastle R-972: Trinnov Optimizer Sony: DCAC = Digital Cinema Auto Calibration Yamaha: YPAO = Yamaha Parametric Room Acoustic Optimizer
Before you run any auto calibration program, it is highly recommended that you read the following threads:
It is important that you follow the following steps before you attempt to run the auto calibration program:
Place your front speakers about 6 feet (1.8 m) to 10 feet (3 m) apart. Make sure the rear of the speakers are a couple of feet away from the front wall.
Do not toe in your front speakers too much. If you want to do this, make sure the speakers are pointing to your shoulders and not your head.
Place your main listening chair/sofa in a location between the two front speakers so that they make approximately an equilateral triangle.
The low frequency sound waves interact with the room boundaries and create standing waves and room modes. Because of these modes, there will be many peaks and valleys of low frequency waves. You should not sit exactly in the middle of a typical rectangular room because that location falls in the valley of many of these room resonances and you will have a hard time hearing any bass. At the same time, you should not sit against the wall as the bass will be too heavy, boomy, and tiring.
Do not place the center speaker inside a cabinet as the cabinet can interfere with the speaker and distort the sound. If you are placing the center speaker under the TV/Screen, put something like door stops under the front of the speaker to point it upward towad your head. If you are attaching the center speaker to the wall above the TV/projector screen, make sure it is pointing downward toward your head.
I highly recommend using room treatments to improve the sound in your HT room. At the minimum, buy absorption panels/foams and place them in the locations to reduce early reflections from the boundaries into the listening area.
Connect all speakers and pay attention to polarity of the seaker wires (positive to positive and negative to negative).
It is highly recommended that you use a subwoofer as the auto calibration programs work best with a subwoofer present. Make sure you connect the subwoofer to the subwoofer output (LFE output) on the back of the processor. If you do not have a subwoofer, it is important that you use front speakers that are capable of reproducing the lower frequencies with ease. In such a case, you must set the front speakers to LARGE. Many receivers/processors will automatically set the front speakers to LARGE when a subwoofer is not present.
The phase control on the back the subwoofers is a usually a simplistic analog control that only changes the phase at one frequency. Proper phase alignment requires that the phase change is different at every frequency. Unfortunately, that is not possible with an analog control. As a result, Audyssey recommends that you leave the phase control at zero.
After all the speakers/subwoofer(s) are connected, go to the processor’s menu and set the subwoofer to YES or NO depending on whether you have or do no have a subwoofer. Make sure all other speakers are recognized properly.
Many receivers/processors may have an option to set the Subwoofer to DOUBLE BASS, LFE+MAIN, or BOTH. Turn that off and set the subwoofer to LFE only. There is a complete explanation of this in the two guides mentioned at the beginning of this post.
USING THE AUDYSSEY AUTO CALIBRATION PROGRAM
The Audyssey room correction program comes in four different flavors: MultEQ XT32, MultEQ XT, MultEQ and 2EQ. Although they are all built on the same basic fundamentals, each receiver/processor may use a different version depending on its DSP processing power. Furthermore, it is possible that some lower end processors may have to turn Audyssey off if you set them to process the bitstream HD audio. Check the owner’s manual for further information.
Quote:
MultEQ XT32: Our newest and most accurate room correction solution with more than ten thousand individual control points allowing finer details of the room’s problems to be captured and corrected. The ultra high resolution filters are applied to all channels including the subwoofers, with the most obvious benefit being heard in the low frequency range where correction is needed the most.
MultEQ XT: Our advanced resolution room correction solution with high resolution equalization filters for satellites and subwoofers. Most products with MultEQ XT are installer-ready and can be calibrated by an Audyssey Registered Installer to provide even higher performance for even the most demanding large or odd-shaped rooms.
MultEQ: Our standard resolution room correction solution that uses mid-level resolution filters for satellites and subwoofers.
2EQ: Our basic resolution room correction solution that uses basic resolution filters for the satellites, but does not apply a filter to the subwoofers.
* Up to 32 measurement positions with MultEQ Pro. Most AVRs with MultEQ XT32 and
MultEQ XT are installer-ready and can be calibrated by an Audyssey Registered Installer to
provide even higher performance for even the most demanding large or odd-shaped rooms.
This page on Audyssey's website gives you all the information about the version of the MultEQ that is available on any particular AVR.
Before you run Audyssey auto calibration program, it is not necessary to turn off Dynamic EQ, Dynamic Volume, or any other options. All internal settings are ignored when the calibration is running, including the volume, level trims, delays, and speaker settings. They are set after you are finished and saved the results of the auto calibration program
After calibration, if you plan to use Dynamic EQ and Dynamic volume, it is a good idea to turn off the Night Mode, Dynamic Range Compression (DRC), and Dynamic Compression (D. Comp) in the receiver/processor as well as the player. In addition, if your receiver/processor has the THX Loudness Plus or Dolby Volume, you should turn them off as these may possibly have an adverse effect on Audyssey Dynamic EQ and Dynamic Volume.
If you have a Bass Shaker, Buttkicker, or Tactile Transducer under the listening sofa/seat, turn it off. The vibrations from them may fool the calibration microphone into measuring and setting a much shorter distance than the actual distance from the subwoofer to the listening seat. It may also result in incorrect equalization for the subwoofer.
Connect the included microphone to the receiver/processor and set it at ear level in the primary listening location. Always start the measurements from the primary listening location and spread out from there. Approximate distance from the first measurement position to any other position is 2 feet (0.6 m), no more than 3 feet (≈ 1m). The first measurement must be taken in the middle of the listening area. After that, the exact location of each measurement is not critical, but be sure to follow the following diagram for proper microphone positioning:
Depending on the version of MultEQ included in your AVR, you will have 3, 6 or 8 measurement locations. With MultEQ Pro software, you can take up to 32 measurements (12 positions are shown in the diagram). Make sure you use all positions for the MultEQ included in your AVR.
You will notice that positions 1, 2, and 3 are located on the seats of the couch. Use a small tripod (see Post #31 for links to a few options) and place it on the couch. If the couch back is slightly higher than ear level, raise the tripod a few inches as reflections from the back of the sofa may interfere with the sound if the microphone is placed too close to it. Since it is recommended that the microphone should be placed as close as possible to ear height, instead of raising it, you can keep it at ear height and move it forward so that it is not too close to the back of the seat. You may also use a boom arm (Post #31 has links to microphone stands and boom arms), but make sure the arm is not in the path of the speakers and also the tripod head should be as small as possible so that is does not interfere with the microphone.
Focus on the central listening area and avoid extreme positions such as the back wall or too far beyond the left and right speakers. The delays and levels for each of your speakers are calculated from the first microphone position. The center position is usually defined as the tip of the triangle with the base of that triangle running through the two front speakers. In an ideal setup, the triangle is equilateral (60° angles). But, in most home theater rooms that cannot always be the case. Even if the seat is off to the side, it is still recommended taking the first measurement location to be in the center of the listening area and then following the pattern in the diagram. The measurements are designed to collect information about the response of your speakers in the room. It's best to avoid placing the microphone in extreme off axis positions because that can give it misleading information about the off axis response of your speakers.
Place the microphone on a tripod for better stability. Make sure the microphone is facing upward toward the ceiling.
Do not place the microphone on the back cushions or the arms of a sofa.
Use only the microphone that was included with your AVR. If the microphone is damaged or lost, contact the manufacturer and purchase a new one. It is possible that some microphones may be compatible. For example, Denon and Marantz share the same parent company and it is more than likely that they use identical microphones.
Unplug any headphones that may be connected to the AV receiver.
Do not stand or sit next or in front of the microphone. Make sure nothing else is blocking the path between the speakers and the microphone. Any changes that you make to the room will require that you run Audyssey again.
Make the room as quiet as possible. Background/ambient noise may distort the measurements. Close all doors and windows, turn off cell phones, radios, air conditioners/heaters, fluorescent lights, light dimmers, or other devices. Radio Frequency Interference (RFI) may cause measurement disruptions.
Do not disconnect the microphone during the setup.
Do not connect or disconnect any speakers during the setup.
Start Audyssey MultEQ as instructed in the manual.
You will hear the pink noise from each loudspeaker until the cycle is finished.
After the measurements for the main position are finished, the following will occur:
Audyssey will report all the speakers it has recognized. If some of the speakers are missing in the list, check the connections and go back and repeat the measurements for position one.
Another very common problem is that Audyssey may report that your speakers are out of phase. Again, do not be alarmed. Always interpret the phase warning by Audyssey with a grain of salt. Complexity of room dynamics and/or some loudspeakers unique crossover/driver arrangements, can trick the auto calibration programs into reporting speakers as being wired out of phase when in fact they are not. Some drivers are intentionally wired out phase. Moreover, it is possible that some amplifiers may invert the signal. If the calibration program reports any of your speakers are out of phase, first check the wiring manually and then use calibration discs such as Avia, DVE, or AIX to audibly confirm the proper phase of each channel. If you checked all your wiring and everything seems ok, just ignore the out-of-phase message.
In Phase Speakers
Out of Phase Speakers
It is important not to confuse phase with polarity. Polarity change is switching the positive and negative speaker wires. A change in polarity only reverses the direction of the frequency wave. Phase shift is a timing difference in frequencies as exhibited in the following diagram. Many factors such as the crossovers, equipment, and the room can affect that.
The weakest link in a loudspeaker is its crossover network. All crossovers create a phase shift of varying degree between the frequencies at the crossover point. Drivers within a speaker are wired out of phase to compensate for that. Also, the interaction inside a subwoofer between the woofer and port can cause polarity reversal warnings. Many auto calibration programs inside the receivers/processors detect the absolute phase and cannot really tell you for sure if the polarity of the speakers are correct.
After you are finished with checking the polarity of the speakers and all speakers are properly recognized, move the microphone to a new position around the listening area and take measurements.
Once you have finished the measurements for all the listening positions, Audyssey will do some calculations for a few minutes and will ask you to double check the settings. You can adjust them later after the calibration for all the speakers is finished. In general, several things may occur:
You may notice that your front speakers are set to LARGE (FULL BAND) or SMALL. Audyssey does not make this decision. Audyssey simply takes some measurements and reports them to the AVR. The AVR manufacturer has complete control over how the speakers should be set. Many of them use inappropriate or archaic rules to set the speakers to LARGE as long as the speakers show some response below 80Hz. You can adjust this later and set your speakers to SMALL. For further information, read the two Bass Management Guides mentioned at beginning of this post.
It is important that you understand that Audyssey measures the performance of the speakers in your room. The frequency response of your speakers in the room as measured by Audyssey may be significantly different than the frequency responses as measured by the manufacturer in an anechoic chamber. Don’t be alarmed. All speakers react with the room boundaries, furniture, and with each other. They exhibit different frequency response in real rooms. Audyssey measures what your speakers are doing in your room and recommends a setting based on their placement. Its results are based on the placement of the speakers and the microphone.
You may notice that Audyssey has reported a much longer distance between your subwoofer and the listening position or a significantly shorter distance between the two. This problem arises because Audyssey MultEQ does not actually measure distance between the subwoofer and the listening area. It measures signal delay. This delay consist of:
The time it takes for sound to travel in the air to the microphone.
The electrical delay in the signal inside the subwoofer:
Any type of filter in the sub introduces delay.
Any type of DSP processing in the subwoofer introduces delay.
The interaction of the woofer and the port in in a subwoofer can also cause problems. This interaction can also cause polarity reversal warnings.
Because of these delays, it is quite normal to see longer distances reported for the subwoofer. You should leave it as MultEQ found it.
When the reported distance is much shorter than the physical distance, then you should worry. Something else has caused that. The most likely cause is vibrations that travel to the microphone through a solid surface such as the floor or the sofa/seat. Sound travels faster in solids than it does in air and this can cause the short readings. The only alternative you have is to try is to make sure that the microphone is isolated from any vibrating surfaces. Avoid placing it on the edge of the listening sofa. Also, move the subwoofer to a different location or isolate it from the vibrations by using a riser.
Once you have finished with the calibration and confirmation, save the measurements to your AVR.
Every time, you move the speakers, furniture, add new curtains or room treatment, you should run the Auto Calibration program again. The crossover recommendations made by Audyssey are based on the measurements in your room. It is not surprising that the roll off frequencies change when you do the above. For example, if the distance from the wall is changed, then it is expected to see a change in the roll off frequency. That is the whole point of measuring and not depending on the the theoretical specifications as reported by the manufacturers.
WHAT YOU SHOULD DO AND WHAT YOU SHOULD NOT DO
It is ok to increase the crossover frequencies of the speakers as set by Audyssey. It is generally not recommended to lower the crossover frequencies below the numbers set by Audyssey. If you do that, Audyssey will not apply correction filters to the frequencies below the numbers that are set by the auto calibration program.
Many people are hung up on the 80Hz crossover frequency that is suggested by most experts. Although 80Hz crossover frequency works for many speakers, it is not a number that is etched in stone. That number was originally recommended by THX and applies to THX certified speakers that have certain frequency characteristics.
Audyssey does not measure the frequency response of a speaker as it was reported by the manufacturer and supposedly measured in an anechoic chamber. Audyssey measures the performance of the speakers in the room and based on that, it recommends some crossover numbers. Depending on their location, proximity to room boundaries, furniture, wall coverings, position of the microphone, etc., even identical speakers may have different performances in the room.
It is ok to change a speaker from Large to Small. For the reason mentioned above, you should not change a speaker that has been set to Small and set it to Large. Always remember that if you have a subwoofer, all your speakers become Small by default.
Do not use Double Bass, LFE+Main, or Both for your subwoofers. Those options will engage Bass Management for speakers that has been set to Large. To understand this, go back and read the two Guides mentioned at the beginning of this post.
Speakers/Subwoofer Distances: Audyssey MultEQ does not measure speaker/subwoofer distances. It actually measures the signal delay. For the main speakers this delay calculation usually results in actual physical distances. But, subwoofers have filters in them that delay the signal more. So, this is equivalent to the subwoofer being further away. It is quite normal to see longer distances reported for the subwoofer.
To summarize, the subwoofer distance calculation is more complex than simply using a measuring tape. Subwoofers have filters in them that add delay to the signal and the auto calibration program compensates for that. That is why you should leave the distances as the auto calibration program found them.
It is ok to double check the speaker levels with an SPL meter after Audyssey calibration is finished. If you are going to do that, make sure you use an external test tone disc such as AIX, Avia, or DVE as the internal test tones of the AVRs bypass all post processing done by the calibration program and will not reflect the true level of the speakers when you play a movie with all the post processing engaged. Furthermore, it is possible that the player and/or cables may affect the actual level of a speaker during playback of a movie. Therefore, it is more appropriate to run the test tones through the same player and cables.
It is important to remember that if you adjust the speaker levels with an SPL meter, you may change the reference level. This means that when you set the master volume to zero level, it may no longer represent the reference level.
After running a MultEQ calibration and turning on Dynamic EQ, if you find the surround speakers to be much louder than the front and center speakers, that is done on purpose. The researchers at Audyssey have found out that human perception of loudness falls off faster behind us than it does in front. So, Dynamic EQ compensates for that using a human loudness spatial model that looks at the master volume setting and makes the appropriate adjustment to the level of the surrounds. This is designed for content where the overall surround impression should remain the same at all volume levels: i.e. surround movies and music.
It is ok to increase the level of the center channel speaker by a few dB's if you feel you are having a difficult time hearing the dialog. Poor response from the center channel speaker is caused due to room acoustics and placement. If a center speaker is placed inside a cabinet or too close to the floor, it can have less than ideal sound.
If the you notice the level of the subwoofer is set to -10dB or a higher negative number in the receiver, it probably means that the level on the back of the subwoofer is set too high. If the level control on the back of the subwoofer is set too high, this can cause the AV Receiver to run out of level correction range when MultEQ tries to set the subwoofer to reference level. Lower the sub level on its back and run the auto calibration again.
If you notice the subwoofer’s level is set too high (e.g., 5dB or more), before you increase the level of the subwoofer on its back and increase the chance of clipping or bottoming, move the subwoofer to a better location. A subwoofer in a corner uses all room resonance modes and will be the loudest. Alternatively, you can use the sub crawl technique. Make sure you run the auto calibration again.
Audyssey applies more correction filters to the subwoofer than the other speakers. It is not a good idea to use a muti-channel speaker setup without a subwoofer or intentionally set the subwoofer channel to NO in the AVR. The filters in the subwoofer channel are designed to only operate in that channel and so they will remain unused if there is no subwoofer in the system.
If you are using a subwoofer equalizer such as the Velodyne SMS-1, REW/BFD, etc., you should equalize your subwoofer(s) before you run the Audyssey auto calibration program. In addition, some of these equalizers have a subsonic filter. If you are using a ported subwoofer, it is a good idea to use this feature to protect the subwoofer from over extension and damage. You should set this filter to 15Hz to 20Hz, depending on the low frequency extension of your subwoofer.
Manual Equalization: After Audyssey calibration, if you decide to perform manual equalization by copying the Audyssey base curve into the manual EQ, this does not copy all the thousands of adjuments points that Audyssey makes. It does not copy the Audyssey filters. In fact, Audyssey is tuned off when you switch to Manual EQ. All you get is a simple graphic equalizer that roughly has the shape of the Audyssey filter in the frequency domain. The time domain benefits of Audyssey filtering are lost.
REFERENCE LEVEL
Reference level is defined for film mixing and movie theaters. Every studio and movie theater is calibrated according to this level. It represents an average of 85dB for the regular speakers on the SPL meter (set on C weighting and Slow) using a band limited (500Hz to 2,000Hz) pink noise at the listening position. The peak level is set 20dB higher at 105db and the LFE peak level is set +10dB higher to a maximum of 115dB. The purpose of the +10 dB gain for the LFE channel is to increase the dynamic range of bass sound such as explosions and crashes. This means when the receiver master volume is set to 0dB, the regular speakers are expected to play a peak level of 105dB and the subwoofer is expected to produce a peak output level of 115dB. This is louder than most people can tolerate, so people normally set the master volume much lower than 0 when watching movies or listening to music. Furthermore, such loud bass level places a heavy burden on the subwoofer and requires multiple high-end subwoofers to produce it accurately.
Because 85dBC test tones can be very loud in a small home theater room and can damage hearing, receiver manufacturers through the encouragement by Dolby and THX decided that a reasonable test-tone level is 75dB and that is the level that most receivers use.
To summarize,
Reference Level is 1.85v line level = 0dB VU meter = 85db playback level.
105dB Peak level = 0dB (Full Scale).
85dB Average Level = -20dB (Full Scale).
75dB Average Reference Level = -30dB (Full Scale).
dBFS (Full Scale) = unit of measure for the amplitude of digital audio signals.
The reference level is "0" dBFS, which is also the maximum signal amplitude that can be stored digitally in a typical digital audio recording system.
Signals louder than 0dBFS just produce clipping (truncation of the waveform, hence distortion).
When calibrating your audio system, the receiver plays pink noise that is recorded at 75dB (-30dB FS). When the individual speaker levels are set to 75dB at the listening position, as measured by an SPL meter, the effects of speaker sensitivity and room acoustics are accounted for and the speakers are all level-matched against the Reference Level.
You can use either the internal test tones of a receiver or an external disc. The internal test tones of most receivers are band limited and recorded at 75dB level (-30 dB FS). External calibration signals on most discs are typically full-range pink noise and recorded at 85dB (-20dB FS). It really doesn't make a lot of difference which method you use as long as all the speakers are balanced. However, it is important to remember that when you play the internal test tones inside a receiver/processor, they normally bypass all post processing, including equalization.
12-12-2010, 06:02 AM
A Guide to Audyssey Auto Calibration & Other Technologies
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