Reference Levels?

[Spiffyfast]

OK, I should know what this is, but I'm still new to home theater. What the heck is reference level, is it a certain spl, or is just louder than normal listening. I listen to everything loud all the time, well at least everyone else thinks its loud...I think my ears are screwed up from my old car audio spl days...but anyway could someone please explain to me what reference level is, I'd just like to know, thanks.

 

[Buckeyefan 1]

The dBr increment is based on the decibel, a logarithmic measure of relative signal strength. Suppose a reference signal has a power of P0 watts, and the signal being measured has a power of P watts. Then the relative signal strength in dBr, symbolized SdBr, is:

SdBr = 10 log10 P/P0

Signal strength in dBr can also be calculated in terms of the effective signal voltage if the impedance remains constant. Suppose a reference signal has a root-mean-square (rms) voltage of V0 volts and the signal being measured has an rms voltage of V volts at the same impedance. Then the relative signal strength in dBr is:

SdBr = 20 log10 V/V0

If the dBr figure is positive, then the measured signal is stronger than the reference signal. If the dBr figure is negative, then the measured signal is weaker than the reference signal.

This may be a little easier.
http://www.soundonsound.com/sos/1994_articles/feb94/decibels.html

 

[Polkfan]

Buckeyefan1,

Cool avatar!

 

[Spiffyfast]

The dBr increment is based on the decibel, a logarithmic measure of relative signal strength. Suppose a reference signal has a power of P0 watts, and the signal being measured has a power of P watts. Then the relative signal strength in dBr, symbolized SdBr, is:

SdBr = 10 log10 P/P0

Signal strength in dBr can also be calculated in terms of the effective signal voltage if the impedance remains constant. Suppose a reference signal has a root-mean-square (rms) voltage of V0 volts and the signal being measured has an rms voltage of V volts at the same impedance. Then the relative signal strength in dBr is:

SdBr = 20 log10 V/V0

If the dBr figure is positive, then the measured signal is stronger than the reference signal. If the dBr figure is negative, then the measured signal is weaker than the reference signal.

This may be a little easier.
http://www.soundonsound.com/sos/1994_articles/feb94/decibels.html

thnx for the info Buckeye, I knew someone would be able to help me out

 

[mtrycrafts]

OK, I should know what this is, but I'm still new to home theater. What the heck is reference level, is it a certain spl, or is just louder than normal listening. I listen to everything loud all the time, well at least everyone else thinks its loud...I think my ears are screwed up from my old car audio spl days...but anyway could someone please explain to me what reference level is, I'd just like to know, thanks.

the short and simple answer is the level at which it was recorded at and played back on the recording studio.

 

[MacManNM]

the short and simple answer is the level at which it was recorded at and played back on the recording studio.

Mtry,
Isn't it different for HT though? I always thought that the standards (Dolby PL, DTS, THX) had their own Reference levels. IE, THX was like 86 DB, SPL @ the listening position.

 

[mtrycrafts]

Mtry,
Isn't it different for HT though? I always thought that the standards (Dolby PL, DTS, THX) had their own Reference levels. IE, THX was like 86 DB, SPL @ the listening position.

Theater mastering is at 85dB spl with a -20dB FS, 105 dB max for speakers and 115 for subs.

At home, because of the nature of the home, not as dead of a space, etc, the test discs are -30dB FS and 75dB spl. But, still 105 dB spl max.
THX for the movies are masterd the same level.

 

[MacManNM]

Theater mastering is at 85dB spl with a -20dB FS, 105 dB max for speakers and 115 for subs.

At home, because of the nature of the home, not as dead of a space, etc, the test discs are -30dB FS and 75dB spl. But, still 105 dB spl max.
THX for the movies are masterd the same level.

Ok, that's pretty much what I thought. So When you do your setup, you should be able to calibrate everything to that output. Hence, you could "dial in" your receiver's volume control, and figure out what reference level is for your system. I.E, on some systems it will be -6db on the volume control, but the same receiver with different speakers might be -10db.

 

[MDS]

Ok, that's pretty much what I thought. So When you do your setup, you should be able to calibrate everything to that output. Hence, you could "dial in" your receiver's volume control, and figure out what reference level is for your system. I.E, on some systems it will be -6db on the volume control, but the same receiver with different speakers might be -10db.

Yes, but here is where the discussion can sometimes get confusing due to terminology. 'Reference Level' (Dolby) is defined as Mtrycrafts said: 85 dB at the listening position when fed a -20 dB FS (pink noise) test tone.

The reference volume position; ie what number on the dial achieves the output reference level , can be set practically anywhere within reason. For example, in the 'modest' system I set up for my sister using an Onkyo 501 (75 watts - let's not rehash the definition of modest. ) I could get the SPL meter to read 85 dB with the volume knob at 50 but the channel trims boosted near their max of +12 dB. Likewise, I could get the same reference level at a volume setting of 60, but with the channel trims lower. So there is some wiggle room as to where you want to set your reference position - it depends on the speaker sensitivity, room size, range of the channel trims, and all that.

For receivers that use the relative volume display, 0 dB is the convention to use, but as you said one could set it up so that -10 dB on the volume dial is your reference. If you were to do that, then 0dB on the volume display would actually be 10 dB over Dolby reference level.

 

[mtrycrafts]

Ok, that's pretty much what I thought. So When you do your setup, you should be able to calibrate everything to that output. Hence, you could "dial in" your receiver's volume control, and figure out what reference level is for your system. I.E, on some systems it will be -6db on the volume control, but the same receiver with different speakers might be -10db.

Well, this is why many/most receivers/processors have trim pots to level match speakers and to give you an ability, limited, to set 'reference level' with the master volume control at the same position. Some receivers dial automatically to 0 on the dial, then you set it up. If you swap speakers, the receiver still turns to 0 but you may have to readjust all the pots, most likely
So, if you want to hear a movie at 'reference' level, you dial in 0. It will be very loud
This way, the master volume control is always at 0 for reference levels. Other receivers may have a differently numbered volume control but the same number should be dialed in for any speakers and trimpots recalibrated.
Hope this and the other post helps without confusing

 

[MacManNM]

Yes, but here is where the discussion can sometimes get confusing due to terminology. 'Reference Level' (Dolby) is defined as Mtrycrafts said: 85 dB at the listening position when fed a -20 dB FS (pink noise) test tone.

The reference volume position; ie what number on the dial achieves the output reference level , can be set practically anywhere within reason. For example, in the 'modest' system I set up for my sister using an Onkyo 501 (75 watts - let's not rehash the definition of modest. ) I could get the SPL meter to read 85 dB with the volume knob at 50 but the channel trims boosted near their max of +12 dB. Likewise, I could get the same reference level at a volume setting of 60, but with the channel trims lower. So there is some wiggle room as to where you want to set your reference position - it depends on the speaker sensitivity, room size, range of the channel trims, and all that.

For receivers that use the relative volume display, 0 dB is the convention to use, but as you said one could set it up so that -10 dB on the volume dial is your reference. If you were to do that, then 0dB on the volume display would actually be 10 dB over Dolby reference level.

People ask this question all the time, I have tried to answer it, however I lack the writing skills to explain these things. I just wanted everyone to understand that when they pull their receiver out of the box, 0db isn't the reference level, nor is it some number designated by the MFGR. There are a lot of variables that go into this.

 

[Spiffyfast]

Awesome, this is the info I wanted to know, ppl say reference level all the time, so i now I know what the heck they are talking about

 

[soniceuphoria]

The way that I always saw reference level to be is that the playback is the same level as the original recording. As stated above the number on your reciever has nothing to do with reference level.

 

[MDS]

The way that I always saw reference level to be is that the playback is the same level as the original recording.

Reference level is specifically defined by Dolby and has been covered. When we talk about reference level, we are talking about the output SPL at the listening position. The SPL at the listening position isn't related to the level of the recording.

Remember that if you are following Dolby reference level, the system was calibrated using a -20 dB pink noise (equal amplitude at each octave) test signal. Real music is a complex waveform that varies widely. The average level of a CD nowadays is -10 dB. Play one of them with the volume knob set to your reference position and the average level at your listening position will be higher than playing the simple test tone.

Ignore reference level for a second. Set the volume to a comfortable level while playing a modern compressed CD with a high average power level like -10 dB. Now switch to a CD recorded in the 80s with a much lower average power level (typically -18 dB) without touching the volume knob. It will be much quieter.