As a former DJ myself, I can tell you that generally promo copies on black vinyl represent a sonically superior copy. Black vinyl records are made like waffles. The stamper is the waffle iron. It’s the metal negative that actually presses the record. The vinyl is the waffle batter, and comes out as a positive copy. Because test pressings are the first ones pressed by a brand new stamper, the sound quality is as good as it gets. Stampers deteriorate over time, and eventually have to be replaced. I've heard 5,000 tossed around as being the average life of a stamper. Of course, some record companies tried to save a buck by not replacing their stampers as often, pressing 6 or 7 thousand copies before retiring the stamper. In this case, the record you bought in the store could have been considerably worse sonically than it should have been. But even with frequent replacement of the stampers, the 3,000th copy is not going to sound like the first 1,000 copies. Since the promo copies are the first pressings (being sent to radio stations and record reviewers) they are generally sonically superior. Occasionally, an album or at least one or two of its tracks may be remixed before the actual formal release to the public, so your test pressing may actually contain a different mix than the one that showed up in the record stores. Also, many record labels released 12-inch singles of whichever cut was deemed to be the big hit on the album, and these 12-inch singles were never sold in stores. With less music crammed onto them (one song as opposed to 12 or so) they often had better dynamic range etc. They were sometimes blank on the other side, or may have had the same music on both sides (in case you scratched one). Frequently, the full-length version of the cut was on one side, and an edited, shorter version on the other. Sometimes these 12-inch singles were pressed on colored vinyl, and may be been issued to the radio stations in plain white sleeves. I have blue, white, gold and a few other colors of vinyl from back in my radio days. My copy of Dave Mason’s “Alone Together” is one of the original so-called “vomit” copies that were pressed on multi-colored vinyl that was supposed to look like marble or something. Later copies were plain old black. My most interesting DJ copy is on gold vinyl with a Columbia label on one side and a Capitol label on the other. It was issued to promote a concert tour that combined artists who were on those two labels.
