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Seeing as how the last version of this became lost, here is a revised version.   Enjoy!

 

Basic Audio Calibration.

This document was originally written by myself (Mark Techer) in 2000 as a part of a larger work titled “Understanding Surround Sound – 5.1 and Beyond”.  That work was later broken into smaller parts and accepted by CEDIA in 2004.   I had posted the original work on DTV Forums Australia in 2006.  Even though it was “pinned” to the top of the page, it seems to have been lost in the transition to Stereo-Net.  I have therefore re-written and updated this work and am making it available to all that require a simple, 10 steps “how to” for calibration of a multi-channel audio system.        

The goal of this document is to allow you to manually set the Reference Level Playback of a Multi-Channel audio system using a Sound Pressure Level Meter and the internal test tones of the system. 
Note:  The Reference Level is 105dB per channel and was set by Dolby Labs in the late 1970s.   

Tools required –

1.       Sound Pressure Meter (preferably with an analogue reading or 1/10th scale digital).  The phone apps that are available via Play-store will work if you have nothing else, but are bit a course as the few I have tested only read in single 1.0dB increments and there does not appear to be additional setting such as A or C weighting or fast/slow response.  Your meter needs to be set to C weighting and SLOW response. 

2.       Tripod or stand to hold the meter.   

3.       Tape measure. 

Procedure –

1.       Once your surround sound system has been connected and tested, you may start the calibration.  If your system comes with an auto calibration mic like Audyssy, YPO etc, you are best to run this first as these systems do a fairly good job at time alignment and may even apply some in room equalization. 

2.       Set the SPL meter on the stand as close to seated ear height as is possible.  The meter should tilted slightly forward and not aimed at any one speaker. 

3.       Place the stand/meter in the primary listening position.

4.       Activate the test tone generator of the audio/visual system.  You may have to manually turn this on but most systems do this when “speaker levels” is selected.  If your system does not default to a 00dB or reference level on the master volume, you may have to manually wind it up to that position.    BE CAREFUL, at this level some of the noise generated may be way too loud and may even cause system damage or failure!  It is not a bad idea to manually reduce the channel trims of your system prior to doing this.  Band limited pink Noise (approximately 400Hz to 2000Hz) should now be heard from the left front speaker.   

5.       Turn on the meter and select the 70dB range (for analogue) and select the C weighting and the SLOW response mode.  On a digital meter, you only need to worry about the high (in excess of 100dB) and low range (less than 100dB).  You should be in the low range on a digital meter as you will dealing with SPL at 75 to 80dB only.  I prefer to use the meter on a stand so that I can step back and not have the meter read reflections off my body.    

6.       With the Master Volume at 00dB, Band Limited Pink Noise playing through the Front Left Speaker, adjust the channel level trim so that meter reads +75dB/C/SLOW.  The tones output by the system should be -30dBFS or 30 decibels below Full Scale.  Full Scale is 105dB and was set by Dolby in the later 1970s where the loudest, undistorted sound will be no louder than 105dB.  The tones output by the system are -30dBFS.  105 – 30 = 75. 

7.       Once level of the Left Front Speaker is set to +75dB/C/Slow, move onto the next speaker (normally Centre Speaker) and work around the system until all channels play back at a reading of +75dB/C/Slow on the meter.  The surrounds MUST also be set at +75dB/C/Slow.  The reason for this is that the level adjustments from the cinema mix to the home have been taken care of in the conversion to the “consumer mix”.  So this procedure applies to all home based surround sound systems, regardless if the systems is a basic 5.1 system, all the way to an 11 channel Dolby ATMOS system. 

8.       The only speaker that is NOT set to 75dB is the Subwoofer (if your system has one).  This is because the wave lengths in the bass region are vastly longer than those in the band limited pink noise and will interact very differently in the room.  The test tone of the SW is not pink noise, rather a “warble” or group of frequencies between 30Hz and 80Hz that have a varying level.  This is help prevent standing waves in the room.  To set the level of the SW to “splice in to the system”, you must set its output to read and average of +79dB.  DO NOT set this to read +85dB on a Sound Level Meter!

9.       Once all channels have been set to the correct Sound Pressure Level, you are almost ready to listen to a sound track.  If your system did not have an auto CAL mic and did not set the time alignment, you will have to manually do this.  Time alignment is simply assuring that sounds arrive at the listening position at the same time.  If you have to use the tape, measure the distance from the listening position to each speaker in the system and set those distance into section usually named “distance” in the set up menu. 

10.   Find a movie you like and play it on your system knowing that you will hear it closer to the way the director intended it to be heard.

Edited by CAVX

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This is how I always used to do it back in the day. I only use the auto stuff for the distance and time, then use the above method for audio calibration. Always got much better results.

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Good to hear.  I did this for a client yesterday and he was most impressed with the end result.  . 

So hopefully this will get pinned here for quick and easy reference.  

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3 hours ago, CAVX said:

Good to hear.  I did this for a client yesterday and he was most impressed with the end result.  . 

So hopefully this will get pinned here for quick and easy reference.  

Hi mark, what are your thoughts on an iPhone 8 and a spl app as apposed to purchasing a spl metre?

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1 hour ago, Hi-Fi Whipped said:

Hi mark, what are your thoughts on an iPhone 8 and a spl app as apposed to purchasing a spl metre?

I think a free app from PlayStore is better than not having a meter at all.  I've got Sound Pressure Level 2017 on my S5 phone for the purpose of showing people that even a free APP meter works and will do the job better than setting levels by ear or relying solely on the Auto CAL with the system. It is a visual reference and no difference to a speedo in a car.  You wouldn't drive without instrumentation and nor should we be calibrating our system without even a basic visual reference.

 

When I checked the APP against my calibrated meter and MINI DSP Mic on the PC with REW, I had to increase the level by about 5dB.  Once set, all seemed good.    

Edited by CAVX

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Moderator

@CAVX pinned it for you :)

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12 hours ago, :) al said:

@CAVX pinned it for you :)

Thank you sir :)

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For those that want to use an APP on their phone, just search "SPL + C Weighting + Slow".  Still free and so much better than the one I initially had on my phone.  Even though it is a digital display, the meter is "analogue" and there is also a small RTA as part of the APP.  Would be very cool if there was a better mic to attach to the phone.  

Edited by CAVX

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