A Loudness Function for Maintaining Spectral Balance at Changing Sound Pressure Levels

Our perception of loudness is a function of frequency as well as sound pressure level as described in ISO226:2003: Normal Equal Loudness Level Contours, which describes the needed sound pressure level for pure tones to be perceived equally loud.
At a music performance, this is taking care of by the sound engineer by listening to the individual sound sources and adjust and equalize them to the wanted spectral balance including the whole chain of audio equipment and surroundings.
At a live venue the sound pressure level will normally change during a concert, and typically increase over time. In this case the spectral balance will not be maintained. If the volume is turned up our perception for especially the low frequency will increase.
If the level is increased 10dB from 90dB to 100 dB a 100 Hz tone will be perceived as +13 dB higher and 50 Hz as +14 dB higher, so an increasing bass boost. (+3 dB is doubling of the effect to the loudspeakers). A level depending digital loudness function has been made based on ISO226:2003, and will be demonstrated. It can maintain the spectral balance at alternating levels and is based on fractional order digital filters.

Tutorial. Abstract T3.3 (30th August 16:00 - 17:00 Open Air Venue)

At the 3rd AES International Conference on Sound Reinforcement -
Open Air Venue 30th August - 2nd September 2017 in Struer Denmark

Different music examples equalized and mixed at a specific mixing level e.g. 85 dBA will be played at different listening levels (75 – 105 dBA) to demonstrate how level will change our spectral perception. An increase in level of +10 dB will at 100 Hz be perceived, as +13 dB (according to ISO226) so increasing the level will give a bass boost. A developed loudness compensation (SpecBal) will be demonstrated, that can maintain the Spectral Balance at changing listening levels. Using dBA measurements challenge the sound quality with hidden ‘free’ bass boost.