#lkfs

As a student, I always find it useful to look at audio delivery specifications to see what is expected by various networks. Here is one for FX/Nat Geo/Speed:

FX/NATIONAL GEOGRAPHIC/SPEED NETWORKS prefers audio to be produced and delivered in 5.1 Digital Surround Sound, prepared for AC-3 Surround Sound transmission. Audio may be delivered in several different formats as indicated below. The audio dynamic range of the material must be suitable for television broadcast. Audio levels shall be measured using the recommended loudness measurement found in ITU R BS 1770 standard, known as LKFS. The loudness is relative to full digital level (0dBFS) and represents the subjective loudness of the audio program.

The loudness shall be measured across all channels (except LFE) using the LKFS technique and averaged across the entire segment or clip. The FX/NATIONAL GEOGRAPHIC/SPEED NETWORKS target loudness level is -24 dB ±1 dB. Instantaneous true audio peaks shall not exceed -2dbFS (BS.1771), while average peak audio levels should not exceed -8dbFS (EBU Tech 3205 or equivalent). Audio should be mixed such that the measured average loudness (using LKFS) of the LT / RT mix shall be equivalent to the measured average loudness (using LKFS) of the 5.1 mix, within ±1dB. The individual channels shall be in-phase to prevent cancellation when tracks are mixed together. Care must be taken to ensure that all elements of the audio are properly prepared, so as not to cancel out if played back in a 2-channel downmix or in a monophonic mode.