Master digital audio with Adobe Audition
This document describes a process for mastering songs for Compact Disc using Adobe Audition. The mastering process is often a long one, and it is not uncommon to spend many hours and dollars to achieve a "commercial studio" sound. With Adobe Audition and the following step-by-step tips, you are prepared to enter the realm of professional music production. Where applicable, we've listed some details regarding suggested frequencies or settings, but every song is different, so use your judgement and, above all, use your ears.
The Mastering Rack
The Mastering Rack, a new feature in Audition 2.0, allows you to apply multiple plug-ins to your material in Edit view and then preview the results in real time. To use the Mastering Rack, import a two-channel stereo mix into the Edit view and choose Effects > Mastering Rack. As a starting point, add the following plug-ins to the Mastering Rack in this order:
1. Parametric Equalizer (see "Pre-dynamic EQ" below)
2. Either Dynamics or the Multiband Compressor (see "Dynamics" below)
3. Hard limiter (see "Limiting/ceiling" below)
4. Stereo Expansion (see "Stereo expansion" below)
5. Parametric Equalizer (see "Post-Dynamic EQ" below)
Note: The Parametric Equalizer functions optionally either pre-dynamic or post-dynamic. Try both to determine which sequence works best for your material.
For more information about the Mastering Rack, see the Audition User Guide, Chapter 7: Applying Effects (page 110).
Sample rate/bit rate
If you recorded into Adobe Audition at 16 bit and you remain in the digital domain, you do not need to increase the bit depth to 32 bit unless you need to do extensive noise reduction. Adding minor EQ or limiting in 32 bit doesn't noticeably benefit most recordings. However, 32 bit does extend dynamic range somewhat and may be worth the conversion if you have ample hard disk space and you are familiar with noise shaping curves and dithering selections.
If you begin at 24 bit or higher, do not convert your material until the final stage of production. For more information, see "Converting back to 16 bit, 44100, Stereo" below.
If you plan to use a limiter (such as the Hard Limiter) or mild compression on your final mix, then you may benefit from accentuating some key frequencies in the compression process. Use the Parametric Equalizer (plug-in) to adjust the following frequencies:
-- 60hs-80hz (bass, 45hs and below from sub-bottom)
-- 250hz (muddiness/low mid)
-- 1.25k-2.5k (vocal fundamental)
-- 5.8k-6.3k (sibilance)
-- 8k-14k (presence and shimmer)
By boosting or cutting these frequencies in very small increments, you can tailor your sound with a variety of narrow and broadband Q. Don't boost or cut more than 3db in any one band (with the exception of cutting the 250hz range if your sound is very muddy).
Use one of the following compression tools to control the dynamic relationship between the quietest and loudest parts of a mix and the relative output:
-- Use the Dynamics Processing plug-in with a compression ratio of approximately 2:1 (a standard setting to give a mix "punch"). Typically, you should not exceed a 3:1 ratio.
-- Use the Multiband Compressor plug-in for frequency-specific compression to achieve an even higher level of control over the mix use. While traditional compressors operate across the entire frequency range, the Multiband Compressor splits the incoming audio signal into 4 user-determined frequency areas so that compression can be applied selectively to each.
In order to compete with commercial CDs, you need to make it loud. The best way to do this is with careful use of the Hard Limiter plug-in. Set the Limit Max Amplitude to -.5 dB to prevents your signal from going over the 0 db limit. If the level is already loud enough, no further settings are required; but you can also further boost the signal by selecting the Boost Input By option. The key is to balance the relationship between how loud the signal is and how close to the Max level (0db) you can get. If you boost your signal too much, you will hear audible artifacts; though, depending on your tastes, you may decide to include these artifacts.
Note: the Multiband Compressor (see "Dynamics" above) has a built-in limiter, allowing you to apply dynamics and limiting with one plug-in.
Stereo expansion (optional)
Many engineers use expansion in the mixdown process (for example, background vocals may be mixed with some stereo reverb, the drums may have some type of presence/ambience effect, electric guitars may bounce left to right). This effect can create a wash of stereo sound leaving you with no center, so use expansion with caution.
If you simply want to widen a narrow stereo field, try the Stereo Expansion plug-in to add depth and dimension to your track. You can also move your center image, but do so with caution to avoid unbalancing your mix.
Post-dynamic EQ (optional)
See "Pre-dynamic EQ" above. If you didn't adjust frequencies before the limiting stage, do so lightly for final adjustments to the mix. Use shaping, but minimal boosting and cutting.
If you increased your max amplitude to -.1, you don't have much room to work with. However, if you added or subtracted EQ, you may want to boost your signal to peak amplitude by normalizing 98%. You can normalize to 100% if you are using a high-quality CD burner and adequate software. The level adjustments in Audition are extremely accurate.
Converting back to 16bit, 44100, Stereo
The preset dither depths and noise shaping curves (pdf=triangular, Noise Shape A) are usually adequate, but may not be so for 32-bit 96k audio. Experiment with conversions on shorter files to find one that best suits your music. For more information on selecting the curves that work best with various sample rates, see Audition Help.
Saving as Windows PCM Wave
To ensure that all CD players capture the start-ID index for your tracks and play them properly, be sure to create wave files with approximately 100-150 ms of space before the beginning of the song. This is not an issue for live recordings with continuous tracks, but you may want to experiment with track spacing.
Using the CD-burning application
The first track on your CD must include a 2-second pause at the beginning. This setting is adjusted in the CD-burning application itself, not in Adobe Audition or on the actual wave file. Write this 2-second gap to your disc just after the table of contents to ensure proper indexing and playback. You do not need to include spacing on any tracks other than the first track. If your CD-burning application supports DAO (disc-at-once), it will create this space for you by default.
If you intend your disc for duplication, burn at 2x or slower (1x, realtime burning); you can burn at 4x for personal use. At slower burn speeds, you have fewer CRC/burst errors. Most plants can detect the speed at which you burned the disc and will not accept a CD premastered or cut at 4x or higher because of the risk of errors during duplication. Most plants prefer green or gold dyes over blue, but you should check with individual plants for specific preferences.
The ability to accurately monitor your progress is a vital part of making the right mastering decisions. Try a different set of speakers (if available) and use speakers and headphones to compare and listen for boominess in the low-end frequencies or tinniness in the high-end. Since part of the goal of mastering is to make the mix sound good in as many environments as possible, make a reference CD of a few tracks and listen to it in a car CD player, a boombox, or a home theatre (whatever you have available). And be sure to give yourself a break! Ear fatigue can set in fairly rapidly during this process, so don't try and beat the clock--make sure you have ample work time but also adequate break time. Mastering is truly an art form, and to master the art form itself takes work, persistence and time.
Here are some other links to related recording subjects.