-Q 33 may not be necessary in metagenomics quality trimming

[qingpeng]

https://khmer-protocols.readthedocs.org/en/latest/metagenomics/1-quality.html

In RNASeq doc, it is mentioned.
https://khmer-protocols.readthedocs.org/en/latest/mrnaseq/1-quality.html

"If fastq_quality_filter complains about invalid quality scores, try removing the -Q33 in the command; Illumina has blessed us with multiple quality score encodings."

Actually this is not accurate. My error is just "Segmentation fault (core dumped)" for not removing "-Q33".

see
http://seqanswers.com/forums/showthread.php?t=9357

"If you use Illumina 1.5+ without parameter -Q33 you get an error message "fastq_quality_filter: Invalid quality score value..." that clearly indicates pitfall.
But in the opposite case, when you wrongly use -Q33 for reads with Illumina quality format, error messages like
Segmentation fault (core dumped)
or
fastq_quality_filter: bug: got empty array at fastq_quality_filter.c:97
do not give a clue what is going wrong.
"