Source Quality And Pre-emphasis
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S
OURCE
M
ATERIAL
Q
UALITY
The DSPX has the ability to substantially improve the quality of your ON-AIR broadcast. However the DSPX can
only work with what you provide it. The best performance will be obtained when the DSPX is fed with very clean
source material. After dynamic multi-band re-equalisation is performed poor quality source material will sound
poorer when processed with the DSPX.
We strongly advise against the use of MP3's and other compressed audio formats for audio storage. If you must
use compressed audio we advise rates of 256 kbps and higher., but linear formats are always to be preferred.
Compressed audio formats employ frequency masking data reduction techniques to reduce the bit-rate. Through
re-equalisation the DSPX can violate the frequency masking characteristics of the bit reduction process, creating
distortion that was inaudible prior to the DSPX processing.
P
RE
-
EMPhASIS
If you are using the DSPX-FM to process for FM broadcast you will need to enable the pre-emphasis filter in the
DSPX.
Even though your STL or transmitter may contain pre-emphasis we recommend disabling it, letting the DSPX-
FM handle the pre-emphasis for the transmission system. The DSPX-FM uses sophisticated processing meth-
ods to limit the high frequency energy of the pre-emphasis curve while maintaining a 'bright' sound.
Using de-emphasis and then pre-emphasising again will only degrade performance and possibly casue over-
shoots, resulting in lower average deviation.
The exception to the rule is when the DSPX-FM is feeding discrete left and right outs to a compressed audio
STL. Bit rate reduction codec's do not cope with pre-emphasis very gracefully and artifacts will be generated.
The best option in this case is to de-emphasise the output of the DSPX-FM prior to the STL system. At the
transmitter site the pre-emphasis can be enabled in the transmitter to restore the processed signal back to nor-
mal prior to transmission.
The best solution is always to locate the processor at the transmission site. This way overshoots are minimised
and quality is maintained.
