Reference Levels - What are they and how to get them

Discussion in 'AV Receivers & Amplifiers' started by flyingalbatross, Feb 20, 2014.

  1. flyingalbatross

    flyingalbatross
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    Given the confusion regarding both 'what' a reference level is and 'how' to achieve it on a home audio receiver, I thought I would have a go at posting a little guide. It is quite long winded but is remarkably simple. Please feel free to reply and correct any mistakes I have made and I will try to update the main post.

    What is it?

    A 'reference' level is simply a commonly agreed upon setup so that playing a source on multiple setups produces the same volumes, peaks and quiets. The most common one used for home cinema is based upon a 'peak' of 105db. This is the maximum which will be touched on with the loudest explosions (i.e. audio signal at 0dB). Most standard dialogue will be intended to come out around 85dB at these levels. (referred to as 20dB of 'headroom').

    The master volume on most AV receivers is referred to as dBFS (decibels Full Scale) and goes from -80 to +20dB or thereabouts. This allows significant adjustment and in principle, the 0dB setting on your receiver plays the sound at the volume it is 'supposed' to be or at reference level. This guide helps you to confirm that 0dB on your receiver is at reference level.

    Most home cinema receivers have a test tone of pink noise, which is recorded at -30dB relative to full scale (simply because listening to a test tone at 105dB isn't going to be comfortable). The principle being you can play the test tone, set your speakers to output 75dB at the listening point with a sound meter and this corresponds with a reference level of 105dB (30+75=105dB)

    How do I do this?
    The explanation below is for a Yamaha RXV-675 but the principle and instructions are much the same. This is all manual setup. It presumes you have already set the correct speaker distance, speaker sizes and crossover points if applicable.

    Start with a decibel (SPL) meter. These can be had for <£10 on amazon or there are free apps available for android and iOS. Obviously the free app and phone microphone are of lesser quality but it's a good start and you can have some form of calibration done in minutes. When using a sound meter don't point the mic at the speaker. Hold it at your listening position (even better - use a tripod) and have the receiver pointed at the ceiling.

    Android - Sound Meter
    Sound Meter - Android Apps on Google Play

    iOS - Decibel 10th
    Decibel 10th on the App Store on iTunes

    The app based ones will usually automatically just give a reading. Real world ones should be set to 75dB, weighting C and slow response.

    The Yamaha test tones are played at a volume corresponding with the master volume setting on the receiver at the time. This needs to be set to 0dB. Be careful not to switch back to audio/TV without turning it down! Other receivers may play test tones at a standard, unalterable volume.

    Open the test tone menu and play them with master volume set at 0dB on the receiver. Measure the SPL reading for each speaker in turn. It should be 75dB.

    For each speaker, alter the levels (this requires exiting test tone menu and adjusting speakers) until every speaker reads at 75dB on the meter at 0dB master volume. Repeat the test tone until you are happy each speaker is set at 75dB from the listening position.

    Subwoofer? Also set at 75dB on the SPL (most consumer aimed receivers set the LFE signal to be 10dB louder than the other speakers to compensate for non-linear low frequency human hearing differences and make your life simpler)

    Pink noise naturally varies by about 2-3dB and so electronic 'fast' meters will waver a bit.

    And that's it! It can be done in minutes and will often throw up some auto-setup incongruities.

    Now listening at 0dB receiver volume should produce 'reference level' dialogue levels around 85dB and peaks of 105dB (it is worth testing on the SPL meter). This is bloody loud and is not recommended. Should you listen at reference levels please expect some angry neighbours and damaged ears. Personally I listen about -30dB for normal TV.

    So why bother? Mainly because setup this way helps iron out any problems where the auto setup mic has incorrectly set levels on the speakers. Using an SPL meter and doing it manually ensures that at your listening position, each and every speaker produces the same volume with a constant test tone, maximising your listening accuracy and pleasure. (incidentally the YPAO in my situation had most speakers set 75-76dB but one was at 80dB)

    What problems will I encounter? this guide presumes that your receiver uses a THX test tone. This appears to be by FAR the most common. If your receiver uses a dolby test tone then it will be at -20dB and you should go for 85dB on the SPL. This is the reason I recommend a test play of some audio and check it comes in around 85dB on the SPL at 0dB volume.

    tl;dr - at 0dB volume on receiver, play test tone and use to set each speaker's levels so they read 75dB on a SPL. Then 0dB on receiver = reference level of 85dB dialogue, 105dB peaks.
     
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    Last edited: Feb 20, 2014
  2. wiz

    wiz
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    Damn you! :mad:
    another trip into the loft to find my level meter and another session of checking my levels:eek::D:rotfl:

    Edit: Very useful btw
     
  3. dante01

    dante01
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    The surrounds aren't technically calibrated to the same levels as those associated with the fronts and if you truly want to mimic what you'd experience in a movie theatre then the surrounds would be set some 2db lower than the front left, right and centre channels.

    Also note that using the pink noise test tone as generated by an AV receiver in conjunction with most consumer level SPL metres will not result in accurate calibration of a subwoofer. In order to obtain accurate and viable results in relation to the sub's output a brown noise test tone would be required. Some degree of guess work has to be applied when using the pink noise tone in order to balance the sub's level in relation to the other speakers and their associated audio channels, either this or you need to use test tones sourced from elsewhere in conjunction with higher quality SPL metres.

    Some may find the following of interest:
    Calibrating Your Audio With an SPL Meter - Blu-ray Forum


    You may also find this of interest:

    Volume Display, 0dB, Reference Level - how is it all related? - Audioholics Home Theater Forums
     
    Last edited: Feb 20, 2014
  4. flyingalbatross

    flyingalbatross
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    yes, and some places recommend setting the surrounds 2dB higher and some people look down their noses at this. It's all personal preference beyond the mechanism of getting everything equal.

    Subs are notoriously hard to calibrate and align with cheap, easily accessible equipment. A lot of people would recommend to ditch the SPL and do it by ear. Setting it to 75dB is a good starting point I think for the purposes of guiding people to do it quick and easily.

    To take it beyond this guide then it's probably worth acquiring high quality demo/reference discs such as Disney's WOW or the THX one along with better quality SPLs.
     

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