Sounds like you’re making progress, @muluoljira. Quality scores in FASTQ data are written using an “alphabet” of 43 characters. In this context, “33” and “64” describe the first ASCII character in the block of characters used in quality scores. (Every ASCII character has a number associated with it. 33 is
! and 64 is
@, so 33-formatted quality scores are written with the characters from
K, while 64-formatted scores use
This bit on Quality Score Variants, which I found in the importing tutorial, gives a high-level overview of which machines use which variants, and is probably your best bet. If you don’t know what equipment was used in sequencing, you could ask your sequencing center.
If that’s not possible, you could preview some of your raw data (e.g.
less my_data.fastq) and compare the quality-score characters to the characters in each format’s group of accepted characters. Hopefully it doesn’t come to that!