SADiE in CD mastering
Introduction
So you've recorded some tracks. The engineer has mixed them down to stereo and they now exist as files on a hard disk.
Now you want to release the album. But how do you get all your individual tracks from your stereo masters onto a CD and into the shops?
You need a mastering studio.
The role of a mastering engineer for album releases requires a combination of artistic and technical skills, and only a full understanding of both will result in a great-sounding album.
Artistic Control
The artistic aspects include:
- Putting all the tracks in the correct order and ensuring gaps between them are appropriate (also sometimes known as sequencing)
- EQing the tracks so that they have an attractive balance, and also to ensure that tracks which may have been mixed in different studios or by different engineers all have a consistent sound. This can either be performed within SADiE's own software processes, via plug-ins, or via an aux send/return loop to external equipment.
- Dynamic range control, to ensure a good perceived listening level throughout the album, while avoiding too low or too high levels.
- Choosing fade in and out lengths and shapes to complement the music.
- Speed and pitch adjustment, and beat-matching of tracks on compilation albums.
- Radio-friendly edits of longer tracks
- Adding appropriate room or hall ambience between recorded tracks.
- Removing media distortions from older tracks, or simply badly recorded ones, such as hiss, crackles, clicks or other unwanted noises – all commonly known as restoration.
- Dithering of material to 16 bit. All level changes, dynamic and EQ processing, and crossfades in SADiE are performed with 32 bit floating point resolution. This results in an internal dynamic range of over 1000dB. As we know, the CD format is limited to 16 bits only, and so the engineer has to ensure that the additional accuracy of the original material is correctly reduced to the 16 bits available on the master. SADiE includes a selection of the best word-length reduction algorithms ever devised, all of which can have subtle but beneficial effects on the sound quality.
All those artistic aspects are subjective – there's nothing you could do to any of the tracks which means these tracks wouldn't actually end up on the disk. They wouldn't necessarily sound very good, but you could still release the album.
Standards Compliant Technical Control
The next set of considerations are the mandatory technical issues which need to be strictly adhered to. Without doing these correctly, your CD won't end up on the shelf:
- Creation and positioning of PQ points. These are the invisible subcodes on the disk which contain the track and index points on a CD. Every CD needs these points in order for a CD to play it. A typical disk has a “start of CD” point, which is Track 1, Index 0. This is usually a 2 second pre-roll which precedes the start of the first audio itself, which is Track 1, Index 1. That's where the CD starts playing from when you press Play.
It's actually possible to extend this gap between Index 0 and 1, so you can hide an additional track before the CD starts playing. To play that track, the listener would have to hit play on the CD, then perform a fast audible rewind in order to access that track. This isn't commonly done, but it's possible if you're mastering directly to Red Book CD.
The end of Track 1 is actually coded as Track 2, Index 0. When this point is reached, the CD player starts counting backwards (the countdown) until the next tract starts at Track 2, Index 1.
If the tracks are continuous, or no countdown is desired, then index 0 and index 1 can be placed at the same location, so the tracks seamlessly count from one track to the next.
Flexibility of PQ index positioning is one of the major reasons why you need to master on a dedicated mastering workstation instead of burning WAV files to a CD in consumer CD burning software. SADiE allows you to place index points freely with relation to the audio – they can even be graphically edited against the audio so you know exactly where each track or movement will start. Consumer software doesn't allow you to put PQ flags within audio tracks, or within crossfades from one track to another. This is why all compilations, live albums, and classical disks need to be mastered on a professional system.
Finally, at the end of the disk, there's a flag which denotes the End of CD. Without that, the CD is unplayable as it is of unknown duration. All these PQ points fall under the heading of Mode 1 data.
- Creation of Mode 2 data. This data records the Universal Product Code of the disk. This is the same data that is often represented by the barcode on the CD cover. SADiE allows the mastering engineer to enter the Mode 2 data, which is then encoded throughout the disk, as data words which appear approximately once every 100 successive subcode blocks.
- Creation of Mode 3 data. This is more commonly known as the ISRC code, or International Standard Recording Code.
The ISRC code is an unique international identifier of every individual audio track. This serves to assist with royalty collection, administration, and anti-piracy measures. Unlike the Mode 2data, the ISRC code remains attached to that track permanently.
The code comprises 12 alpha-numeric characters, set out in a standard format:
AA – A01 – 23 – 45678
The first two characters are the Country Code, which stores the registrant's country. The next three characters are the Registrant Code (sometimes known as Owner Code), which stores the details of whoever is the track registrant at the time of ISRC code allocation. The next two characters are the Year of Reference Code, marking the year of the track's release. The final 5 characters are the Designation Code. These are ideally sequential numbers on an album, and form the final part of the ISRC code for that whole track. Although there are only 5 characters, it is possible to repeat the same numbers in a subsequent year, as the ISRC as a whole must be unique. It's up to the registrant to ensure that their company doesn't create duplicate codes during any single year.
SADiE allows the manual input of ISRC codes attached to each Index 1 point of a track. (It is not part of the CD specification to have more than one ISRC code per track – that would be pointless.) Alternatively, the operator can input and store the Country and Registrant Code, and SADiE will automatically create sequential numbers for all the tracks on the album.
Creation of the final master.
This can be in many formats, and the exact one used is often dictated by the requirements of the pressing plant of factory which you use to press the CDs.
The first method of delivering masters to a pressing plant predated recordable CD media. Way back then, the only available digital audio mastering device was built around a modified video tape recorder, that being the only format with enough data storage capability to handle the emerging digital formats and their associated high data rates. Sony's solution was one of the most popular, based on their U-matic tape machines with a digital audio conversion unit. To create one of these tape masters, you needed to connect audio, timecode, and RS422 cables between SADiE and the U-matic, sync them together, squirt an audio-coded burst of data to the tape which included all the Mode 1-3 information, and then start the audio at 2 seconds precisely. Of course, this was a real time process, and it was very expensive. But for the first few years of CD production, it was the only way.
Then came recordable CD. Suddenly, submitting a master as a Red Book CD-R was the simplest method. SADiE allows you to burn a disk with all the relevant technical data, and then you send that to the factory for them to copy into their pressing equipment. However, the CD format and channel code is a consumer product. It was never designed to be 100% data accurate, as it allows for replay interpolation of audio as well as actual error correction. So although a disk would play back with no audible errors, it might not be exactly the audio you sent the factory. So although sending a CD-R is universally accepted, there are better and more secure methods.
The next step was to record the PQ information and the audio data (disk image) to an 8mm data tape. This was stored in a format called DDP, or Disc Description Protocol. The most common brand name for these tapes was Exabyte, and their advantages compared to recordable CD include 100% data integrity with verification routines, and as the tape was enclosed within a data cartridge originally designed to store banking and financial data, it survived transportation and handling much better than the open and comparatively fragile CD-R. At the time, the capacity of these tapes seemed enormous, as they could be up to 2-3 times the size of an album. But as the demands of the global storage industry increased, it became uneconomical for Exabyte and other companies to continue the manufacture of what now seemed tiny drives and tapes, and the format was dropped. Many factories still accept DDP on tape, but the format is waning as old drives become uneconomical or impossible to repair.
With the advent of recordable DVD drives in computers, SADiE introduced support for writing of the DDP disk image to DVD-R. This was very similar to the data which had been previously sent to the Exabyte 8mm tape, and allowed data with 100% integrity to be stored on the DVD disk. However, this still suffers from the same vulnerabilities as CD-R, in that fingerprints, dust, or transportation damage can cause the disk to be rejected at the pressing plant.
So most recently, plants have started to accept the DDP image via secure networking or FTP transfer. SADiE creates a master disk image which is then verified with a checksum algorithm. The image and the checksum is then uploaded from the mastering studio to the factory, where an engineer can re-verify the image and produce his own checksum. If that is identical to the checksum supplied by the mastering studio, then you all have the confidence that the file has been successfully transferred from the studio to the factory with 100% data integrity.
Other CD formats
- Red Book CD is the specification for the most common type of audio CD on shelves, i.e. audio and CD-Text. SADiE supports writing of CD Text so that alphanumeric text may be displayed on compatible CD players. Typically the type of player that supports CD text are in-car CD players, although the advent of media players in computers opens up the potential for text display on screen. Still relatively rare, SADiE is one of the very few professional mastering systems that can create CD text within a master.
- Orange Book CD is not usually used for commercial releases, as it is less flexible about its PQ flag positioning than Red Book. For example, it does not support countdowns between tracks, and an Orange Book disk is usually burned track by track, rather than disk-at-once. Orange Book is the format used by standalone CD recorders such as Marantz, HHB, Pioneer etc, where the disk is created by pressing Record and Stop as on a tape recorder. SADiE supports Orange Book for track-by-track creation of disks, maybe for burning sound effects onto disk at the completion of each sound design project.
- Blue Book CD is sometimes known as Mixed Mode CD. This is where an audio disk plays as normal in an audio CD player, but when the disk is inserted into a Mac or PC, additional CD-ROM data is then available. This could include compressed versions of the audio, video files, graphics, band data, links to web sites, or any other data which could accompany the music. To create a Blue Book disk, a switch within the SADiE mastering page enables the engineer to write the audio portion of the disk first, and then subsequently add the CD-ROM data.
Finally, one little issue which you might be interested in. The sound quality of all SADiE systems is truly excellent and worthy of the most high-profile, world class releases.
The SADiE offices are staffed by people with many years' experience of professional mastering techniques, and SADiE itself has been at the technological cutting edge of mastering with digital workstations for over 15 years. If you need any advice, don't hesitate to contact us.
