Software Dolby-B|C Compatible Compander

  DDi Codec is a precise digital equivalent of Dolby-B/C analog tape noise reduction system. It is the world's first dedicated software capable of decoding or encoding Dolby-C formatted audio in digital domain, along with full backward compatibility to Dolby-B. Powered by the proprietary DSP engine, the decoding or encoding can be performed in real-time pace, which allows instant monitor and control of quality.
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The software also comes with an unique set of fine-tuning tools for reducing tracking errors in practice. Deeper optimal result can be achieved by effectively using the tools, as specified below:

  • The "Reference Vernier" is a novel widget for determining Dolby Reference Level in an interactive and progressive manner. It supports either objective calibration (with Dolby Tone) or subjective estimation (without Dolby Tone).

  • The azimuth and gap-loss compensation tools are the digital efforts of remedy in compensating minor imperfection of an analog tape player used for digitizing audio tapes.

  • The "Play Trim" is another digital tool for compensating weakened signal often found with a degraded pre-recorded tape.

  • The EQ Converter offers digital translation between 120μs and 70μs IEC tape equalization formulas — if such a flexibility is not offered by a given tape player/recorder.

  • The built-in tone generator offers 400Hz 0dB signal at Dolby Reference Level for easy calibration.
These fine-tuning tools can work independently of the Dolby-B/C codec, which can also be applied for refining non-Dolby formatted audio.

DDi Codec is a stand-alone GUI app without relying on any other DAW host. It let the computer perform as a outboard Dolby-B/C NR unit in one of the following 4 working modes:

  • Audio-In to File (a digitizer/recorder).
  • File to Audio-Out (a player).
  • File to File (an off-line processor).
  • Audio-In to Audio-Out (a through processor, with slight delay).

Currently supported audio formats are: WAV, MP3, FLAC, AIF, AAC and M4A, up to 96k/24bit.

  Audio Demo #1 (Symphony)
Audio Demo #2 (Electronica)
Audio Demo #3 (Vocal)

What quality can be expected from DDi Codec software compared to an analog Dolby-B/C hardware?

Analog hardware was the native form of Dolby-B/C system. As of today, using analog Dolby-B/C hardware is still the best choice in theory. However, physical components in analog hardware may not stay consistent over time. In fact, vast majority of the analog Dolby-B/C hardware found today were produced decades ago and missing regular maintenance as required. They might drift out of the original specification more than one can anticipate, causing Dolby mis-tracking and muffled sound. The hardware here refers to tape recorders/players with built-in Dolby-B/C circuitry and external (outboard) Dolby-B/C analog companders.

Particularly during decoding, even a well calibrated Dolby-B/C hardware may not guarantee an optimal decoding result because audio signal on a given tape might degrade over time or it was simply encoded by a degraded encoder in the first place. It becomes a common practical need for a decoder to be able to compensate all the errors (as much as possible) at the end of the entire chain. This practical need can hardly be satisfied by using a typical analog hardware that is only calibrated to a standard.

Interchangeability is another issue found between different Dolby B/C hardware devices that was largely overlooked. Audio content that was encoded by a hardware device may not sounds perfect when being decoded by another device of different manufacturer/model/series. The fact can also be observed by comparing the factory data sheet with the standard data published by Dolby Labs. A few early Dolby ICs used in those analog devices were found with too much full-range tolerance, means, even after being calibrated to the standard reference level, their frequency characteristics/dynamics on other lower signal levels deviated too much from the standard in their own ways, causing interchangeability issues.

DDi Codec is created as a digital alternative especially for those who are not fully satisfied/confident with the aged analog Dolby-B/C hardware but are willing to accept digital help. Compared to analog hardware, DDi Codec will never drift off design specification over time but also offers additional flexibility in working with imperfect tape players and/or degraded pre-recorded tapes, getting the most out of them. The software is carefully crafted with full respect to the original Dolby-B/C system topology and quantitative understanding of the original analog circuitry. It takes an innovative/proprietary approach to overcome the unique challenges in reproducing the unique non-linear characteristics with DSP (Digital Signal Processor). The development was driven by science rather than subjective approximations.

The software will operate as a typical outboard (external) Dolby-B/C compatible compander which offers better flexibility/potential to achieve optimal result (than an on-board counterpart) with the convenient calibration options exposed to user. As a software solution, it is for the first time to allow Dolby-B/C decoding/encoding being able to cross-inherit the digital advantages, such as: lossless fidelity, zero new noise, mathematical accuracy, wide dynamic range, low cost, no wear and no maintenance. The software also makes it possible to restore existing digital archives (audio files) which are still encoded in Dolby-B/C, removing the hard pre-emphasis artifacts which was otherwise impossible without re-digitizing the original analog tapes. The file-to-file decoding can be done much faster (by several times) than using a real-time-only hardware. For studios/publishers, the software allows direct encoding the digital master copy and feed it straightly to a digital capable duplicating system, avoiding unnecessary analog processing and perhaps offering alternative licensing solution too.

Since the official program for granting Dolby-B/C license has been long closed, it is impossible for DDi Codec to claim any official proof of quality. Use of this software is still at user's own risk. However, its performances have been measured and summarized in the following data sheets, along with online audio demos. Hope they can help in relaxing the stress of making choice between the new software and the traditional hardware.


The measured self-encoding then self-decoding curves have been omitted from here because they are almost perfect flat lines.

Finally, while DDi Codec is intended to be a precise digital equivalent of the analog Dolby-B/C system, it may not incidentally enhance "analog taste" of the digital audio which is rather a subjective matter.

Audio Demo #1 (Symphony)
Audio Demo #2 (Electronica)
Audio Demo #3 (Vocal)

Dolby-B and C are the tape noise reduction systems developed by Dolby Laboratories.

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