Optimize your mix for data-compressed release formats
Fig. 1. Codec Toolbox lets you hear how your mix will sound when processed by different codecs before the fact. The included Codec Toolbox Manager encodes and decodes audio and edits metadata. CODEC TOOLBOX is a lite version of the pricier Sonnox Fraunhofer Pro-Codec, but it’s no slouch. The Codec Toolbox plug-in lets you audition, in real time, how different codecs will make your mix sound before it is rendered (see Figure 1). This removes the guesswork from creating different mixes or masters that are sonically optimized for each data-compressed release format, such as MP3 or iTunes Plus.
Once your mix is tweaked to perfection, use the included Codec Toolbox Manager standalone application to encode your mix and add metadata such as the song title and artist’s name. Codec Toolbox Manager can also perform batch processing and decode data-compressed files into WAV or AIFF format.
Codec Toolbox and Manager support 32, 44.1, and 48kHz sampling rates and 16-bit audio, and will automatically dither and truncate to 16-bit if necessary. (Pro-Codec can encode higher-resolution audio, but doesn’t offer metadata editing or batch processing.) I tested V1.0.3 of the software bundle using Digital Performer 8.05 and Mac OS X 10.8.5.
Put it There Codec Toolbox should be placed on the last insert slot for your master output. While I mixed or mastered, I could switch back and forth between hearing the effect of the plug-in’s requisite 16-bit word-length reduction (pre-codec input) and post-codec output for comparison purposes, using buttons in the plug-in’s GUI.
While my DAW played back, I selected from the plug-in’s pop-up menu the MP3, AAC-LC, HE-AAC, HE-AAC V2, and Apple AAC (iTunes Plus or Mastered for iTunes) codecs in turn to hear how they made my mix sound. Where the selected codec offered alternate settings, I could choose either constant- or variable-bitrate mode, and the specific bit rate I wanted to hear (for example, 256kbps for MP3). The HD-AAC codec—which includes both a lossless and lossy core—is also included solely for the purpose of auditioning its 16-bit input signal; its actual lossless core can’t be auditioned, but you can hear its lossy core by auditioning the AAC-LC codec in constant-bitrate mode.
Any codec can sometimes cause clipping when fed a hot signal. Codec Toolbox’s Overs meter and associated clip LED (both featuring adjustable peak-hold time) showed the post-decoder level. This invaluable visual feedback alerted me that I should lower my master’s output level 0.8dB to preclude iTunes Plus encoding causing distortion.
An NMR (Noise to Mask Ratio) meter indicated whether my selected codec was causing audible artifacts in any of nine frequency bands. This was most likely to occur with a very low bit rate selected (which is unavoidable when using either generation HE-AAC codec). The only consistent solution I found was to choose a higher bit rate; in my experience, you can’t EQ a mix differently to prevent these artifacts.
Saving Time and My Neck In Codec Toolbox Manager, I could see how big the file size would be for the currently selected codec, mode, and bit rate before rendering the file—a big time-saver when preparing files for websites with upload-size restrictions. I encoded the audio in the compressed-data format I’d mixed for, adding metadata to the file before rendering. I could also edit metadata in pre-existing MP3 and M4A files.
For archived, full-resolution masters not prepared while using Codec Toolbox, activating the Manager’s Clip Safe button automatically applied the correct amount of gain trim needed during the encode process to avoid clipping the chosen codec. This is just one of the many ways in which Codec Toolbox saves time and prevents heartburn. Costing only around $58, Codec Toolbox is a steal!
STRENGTHS Realtime auditioning of multiple codecs. Offline encoding and decoding. Batch processing. Automatic level optimization. Writes and edits metadata.
LIMITATIONS Doesn’t support sampling rates above 48kHz. Dithers and truncates greater bit depths to 16 bits.
£35 (~$58 USD) direct, online price