Bear Family begins Acoustic Blues, their 2015 companion set to their 2012 Electric Blues series, in the two decades prior to World War II: the 1920s and 1930s. Each decade gets a disc on this double-CD compilation and producer/annotator Bill Dahl has a sharp eye for both major figures and standards, providing just enough well-known songs to serve as mile-markers between the lesser-known sides. This is, after all, designed as a textbook, a quick yet thorough voyage through the past that serves simultaneously as introduction and instruction. Dividing the collection into specific decades helps untangle some of the mangled threads of history, particularly for listeners who tend to group prewar acoustic blues into the same group. Here, it's easy to hear how particular styles developed on record, to realize that the '20s were devoted primarily to solo recordings and supporting instruments surfaced in the '30s, such as the violin on Mississippi Sheiks' "Sitting on Top of the World." Also, the sequencing makes the introduction of the now-familiar lower-string shuffle on Johnnie Temple's "Lead Pencil Blues (It Just Won't Write)" a revelation, just like Robert Johnson's appearance toward the end of the collection helps place his rise in context; he may have been an integral part of acoustic blues' foundation, but he was not the start, he was part of the continuum. What is so valuable about Acoustic Blues, Vol. 1 is that it illustrates that continuum through expert song selection and annotation, providing an immersion that is illuminating and entertaining.