Remastering using Sound Architecture
Below is a description of a typical process and philosophy I employ when remastering. It pertains specifically to a recent CD remastering project I undertook for the CD "Sondes" by Electro-Acoustic Composer Randall Smith.
In remastering the works on Sondes I was primarily concerned with enhancing the clarity while revealing as much of the sonic detail as possible in each composition. To accomplish this I created a series of proprietary software processes to be performed in non-realtime mode. These custom processes are not compromised by the limitations imposed by realtime mode, and result in superior enhancements of sound quality. The tasks of each of these processes and their affects on sound quality and compositional detail are described below.
Equalization is the first signal processing performed. It was performed in 32/64-bit floating point with FIR filters (phase linear filters). Before optimizing the sound of each recording a very accurate analysis of what the actual overall spectrum of each track was first required. The strategy of the equalization was to balance all the frequencies present in the signal so that all the components would be heard with no dominate frequency band masking or overpowering any other frequency bands.
The removal of the frequencies below the audible range was also performed with high-quality digital high-pass filters. This was useful because a common result of intensive sound editing and mixing of music, especially in the composition of electroacoustic music, is the creation of sidebands, particularly in the frequency range between 1 and 20 Hz. Virtually any fade in/outs contain a broad range of frequency components with a pronounced emphasis in the sub-audio band. The manipulation of these 'control signals' (fade in/out) upon the audio signal superimposes the control signal spectrum onto the audio spectrum. The complete removal of these frequencies added clarity and dynamic range while preserving the loudspeakers when this music is played at high levels.
Reverberation was also added to the mixed electroacoustic works Continental Riff, Convergence, and Liquid Fragments, in order to add spaciousness and depth to there overall sound. A custom reverb signal, or impulse, was generated with spectral properties designed to enhance but not interfere with the direct (original) signal. The reverberation signals were mixed at low levels (-19dB) relative to the original signal. The reverberation signals have midrange and treble emphasis (with much less energy in the bass region). This type of reverberation spectrum was chosen to enhance the clarity of the transients yet add a spacious component to the overall sound. The stereo field of the reverberation signals was designed to minimize the image smearing by having the reverberation signals positioned at the same point in the stereo field as the source instrument. In other words, if an instrument sound was heard at the extreme left channel the reverberation of that signal was also heard only at the extreme left channel. The process of preserving the stereo field added depth to the composition while maintaining the clarity of the original performance and composition.
A dithering signal was used to convert the 3-bit floating point signal into the final 16-bit soundfiles for the final CD. A proprietary process of extracting the 8~12dB below the 16-bit signals noise floor (in the original 32-bit floating point soundfile) and adding this music into the lowest 8~12dB region of the final 16-bit signal was also performed.
Finally, the bringing together of these processes in an effective way was as much a pleasure as a challenge. The repeated listening required for this remastering gave me the chance to appreciate the rich sonic layers developed in Randall Smith's music. Working with contemporary composers gives me the first hand opportunity to witness as well as participate in developing technology for music.
Ernest Cholakis, Numerical Sound, Toronto, September 1999