One of the most important resources for all Trad Lovers is a good set of the recordings Louis Armstrong 
made near the beginning of his career under his band called The Hot Five and Hot Seven. Recorded between 1925 and 1928, these recording formed the foundation for jazz and are so historically relevant that most serious musicians use them as a learning tool even today.
The process of recording them however was not standardized and the actual set of recordings were often sped up to make them sound more exciting, or to fit the constraint of the recording medium of the day. Three minutes is all that would fit on a recording.
Some years ago a famous German company, Deutche Gramaphon released a boxed set of these recordings that have been speed corrected and remastered so they sound exactly as they did in the recording studio. If you are interested in collecting these recordings, this boxed set is the one I recommend to everyone and can be easily obtained from Amazon.
If you are a musician trying to play with the recordings, like me, this set is indispensable because they will all be in tune instead of a ¼ step sharp like other released recordings of this collection. I hope you enjoy these and happy listening!