Quality Control, or QC, is an important part of the production process. At Airshow and other professional mastering studios, as well as record labels, every master is put through a systematic QC process.
QC for CD and digital release
At Airshow, we listen to the masters to make sure there are no anomalies that escaped notice during the mastering session or were introduced during the creation of the masters. We also check metadata (CD Text and ISRC codes) for accuracy, and verify the placement of CD track markers. Masters for DVD, Blu-ray and film are checked for proper audio/video sync. Physical masters—usually CD-Rs—are analyzed for errors in the media itself. For masters delivered digitally, we generate MD5 checksums for each file. (A checksum is a number representing the sum total of the characters in the file; it won’t match if there is a change in the file.)The checksums are used at the receiving end to insure that no errors were introduced during the up- and downloads.
If any errors are found during QC, the master is sent back to the mastering engineer for correction. If a project requires masters for multiple release formats—CD, high-resolution downloads, LPs—each of these masters is QC’d. This way we insure that your valuable masters are error-free and ready for release.
All of our QC steps, and those that are performed at CD manufacturing, happen behind the scenes and don’t directly involve the client.
QC for vinyl release
For LPs, the QC situation is different, and does involve our clients. Production of vinyl records involves several mechanical steps, and problems can creep in during any of them. Clients releasing vinyl have two opportunities to check their projects.
The first step of vinyl production is cutting the lacquers. Vinyl cutting engineers can cut a “test lacquer” or “acetate” for the client to assess the disc cutting process. Before the days of digital production, when the cutting engineer was also the mastering engineer, a test lacquer served the same purpose as the reference audio we send clients to review and approve. There are questions about whether QC’ing test lacquers is worthwhile today.
The cutting engineer creates the “master lacquer” which is shipped, without delay, to the pressing plant. At the plant, mechanical processes create metal parts used for pressing. A very short run of “test pressings” are made and sent to the client to evaluate. It is absolutely essential to listen to the test pressings. Upon approval of the test pressings, the complete production run is pressed.
We asked Kevin Gray, a veteran cutting engineer at LA’s Cohearant Audio for his thoughts on QC for vinyl releases. “I personally don’t recommend acetate refs [test lacquers], at all, for the following reasons: They are a much softer material than vinyl and play very differently. They don’t reveal problems with vocal sibilants, because the acetate is soft, compared to the final pressing. They tend to skip and mistrack compared to a pressing for the same reasons.” In addition to costing time and money in the production process, in Kevin’s opinion, test lacquers can yield both false positives and false negatives. “Having a ref cut during the lacquering, or after, is a complete waste of money considering that a test pressing will reveal many things an acetate can’t.”
At some cutting studios, once the acetate is sent for approval, the whole project goes back in the queue. Even if the client approves quickly without revisions, it can take a week or two for the project to emerge at the front of the line to have the lacquer master cut and sent to the manufacturer. Be sure to discuss the cutting studio’s policies and lead-time so you know how these QC steps will affect your release schedule.
QC at the pressing plant
Some pressing plants, but by no means all of them, perform quality control on test pressings before they ship. Someone at the plant listens end to end to a pressing, and if they don’t hear flaws (ticks or pops are the most common flaws), they either send test pressings to the client if requested or move directly to manufacturing. Some pressing plants do not listen to a test pressing, and rely on the client—or the client’s engineer—to perform the quality control. Be sure to ask your plant what their practice is.
How to listen to a test pressing
At Airshow, we listen to the test lacquer (if any) and the test pressings in the same studio where the project was mastered, so we can directly compare them to the digital master approved by the client. Kevin concurs with Airshow’s practices for QC of test pressings: “If you and the client are relying on the test pressing [usually 10 -12 discs] from the plant for QC, it’s important to know what to listen for. Unless the first disc you listen to is flawless, it is imperative to check more than one. I suggest listening to the first one all the way through.” Flaws to listen for include any noise not apparent on the digital master. “Note any flaws by stopwatch from the start of each song, and if any flaws are found, check those times on a second pressing. It the flaw is only on one pressing, it is an anomaly of that pressing. If it is on both, it is a flaw on the metal part.”
The client or engineer contacts the plant with the precise timing and nature of the anomaly and the plant will check for it on their metal “mother.” Sometimes they can repair the part; sometimes they will choose to simply recut. In either case, the client needs to audition another set of test pressings. Because the flaw originated at the pressing plant, the response should be prompt and not introduce a lengthy delay in production.
In our earlier blog post about vinyl production (How to Plan a Vinyl Release Without Delays or Headaches), we recommended working only with cutting engineers and pressing plants that have good reputations, as the vinyl process is complex enough to invite errors. If clients want to forego the test lacquer from the cutting engineer and go straight to the master lacquer, it’s all the more important to know who is cutting your project.
With or without the test lacquer step, Airshow engineers are in a good position to QC the steps along the way in the vinyl process and communicate with the cutting engineer or the pressing plant on your behalf to get a vinyl release as pleasing as your CD release.
Contact your Airshow mastering engineer or studio manager to talk vinyl!
Want even more information? Kevin Gray authored a paper while at RTI (pressing plant) called “Producing Great Sounding Phonograph Records (or Why Records Don’t Always Sound Like the Master Tape)” back in 1997. It’s still on the website: http://www.recordtech.com/prodsounds.htm