## Topic: Help needed for Gain calculation for audio signal for target loudness (Read 2380 times)previous topic - next topic

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• garfield85
Help needed for Gain calculation for audio signal for target loudness
##### 18 January, 2012, 03:43:58 AM
ITU standard talks about loudness calculation of audio signal. EBU mainly talks about programme loudness, LRA and true peak calculation and also gives standard acceptable value for programme loudness (-23LUFS).
It also says if the programme loudness varies from this value, the signal must be amplified/attenuated to achieve target value.

My question is how that gain is calculated to be applied to audio signal?
Ex. If programme loudness comes out to be -18LUFS, this means I should give 5LU attenuation to my audio signal.
So, what this "5LU" transforms to in time domain so that I can multiply this to my audio signal?

How this is calculated and if there is any document/spec etc explaining this would be helpful.

• [JAZ]
Help needed for Gain calculation for audio signal for target loudness
##### Reply #1 – 18 January, 2012, 02:03:17 PM
The simple answer is that LU is like dB. I.e. it is a logarithmic scale.

There are people here more knowledgeable in this area, which I hope they will give the correct values, but this is how to calculate it based on dBs:

This is C code for conversion of dBs:

/// linear -> deciBell
/// amplitude normalized to 1.0f.
float inline    dB(float amplitude)
{
return 20.0f * std::log10(amplitude);
}

/// deciBell -> linear
float inline    dB2Amp(float db)
{
return std::pow(10.0f, db / 20.0f);
}

• chi
Help needed for Gain calculation for audio signal for target loudness
##### Reply #2 – 18 January, 2012, 02:35:34 PM
For a more formal specification, see EBU Tech 3343 (Practical guidelines for production and implementation in accordance with EBU R 128), especially section 6.2 scenario b. It also says in section 2: “For relative measurements, Loudness Units (LU) are used, where 1 LU is equivalent to 1 dB”, which is essentially what [JAZ] wrote above.

• garfield85
Help needed for Gain calculation for audio signal for target loudness
##### Reply #3 – 19 January, 2012, 12:23:45 AM
Thanks for the reply. I have gone through EBU tech 3343 and was thinking of the same but the loudness calculation is quite different than simple logarithmic calculation.
According to ITU BS.1770-2, the loudness calculation uses K-filtering, mean square, then weighted gain to each channel and then its summation.
My doubt is, its conversion back to time domain could not be simple anti-logarithmic scale.

Ex. if my signal needs +5LU gain then i doubt that simply multiplying each channel with "pow(10.0, 5 / 20.0)" will be enough.

• pbelkner
Help needed for Gain calculation for audio signal for target loudness
##### Reply #4 – 19 January, 2012, 01:48:06 AM
How this is calculated and if there is any document/spec etc explaining this would be helpful.