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Notes from DL1YCF (Start)
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The material put into piHPDSR is meant as a minimal model for the ease of the user,
it is generally recommended to use "installed" versions of RNNoise compiled
with CPU-specific optimisations etc.

The RNNoise code within pihpsdr comes from

https://github.com/xiph/rnnoise.git

A new "Makefile" has been provided that just compiles the files needed with standard
optimisation levels. This means, that only the file

rnnoise/Makefile

within the pihpsdr directory differ from those in https://github.com/xiph/rnnoise.git.

The RNNnoise model is not contained in the above repository but downloaded during
installation of rnnoise. The model is originally contained in the files

rnnoise/src/rnnoise_data.c  (originally, 80 MByte)
rnnoise/src/rnnoise_data.h  (1 KByte)

The file rnnoise_data.c (80 MByte) is not only larger that the recommended
maximum file size in github (50 MByte), its compilation runs out of memory
on RaspPis with only 1 GByte of main memory. Therefore it has been split
into six parts. This means, rnnoise_data.c has been changed (it is now only 
16 KByte long) and most of its contents have been moved to the following
six header files:

rnnoise/src/rnnoise_data_1.h  (16 MByte)
rnnoise/src/rnnoise_data_2.h  (13 MByte)
rnnoise/src/rnnoise_data_3.h  (12 MByte)
rnnoise/src/rnnoise_data_4.h  (14 MByte)
rnnoise/src/rnnoise_data_5.h  (11 MByte)
rnnoise/src/rnnoise_data_6.h  ( 9 MByte)

The following six *.c files, each of this is < 100 Bytes long, each include one
of these header files and can be compiled separately:

rnnoise/src/rnnoise_data_1.c
rnnoise/src/rnnoise_data_2.c
rnnoise/src/rnnoise_data_3.c
rnnoise/src/rnnoise_data_4.c
rnnoise/src/rnnoise_data_5.c
rnnoise/src/rnnoise_data_6.c

These changes now make it possible to compile pihpsdr with rnnnoise on a RaspPi
or a RaspPi ComputeModul with only 1 GByte of main memory.

Consequences:

Upgrading the model (that is, adapting a new file rnnoise/src/rnnoise_data.c) is somewhat
involved. Upgrading rnnoise itself (*.h and *.c files in rnnoise/src other than rnnoise_data.c
and rnnoise_data.h) is straightforward.

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Notes from DL1YCF (End)
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