Software Dolby-B|C Compatible Compander

  DDi Codec is a precise digital equivalent of the traditional 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/encoding can be performed in real-time pace, which allows instant monitor and control of quality.
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Deeper optimal result can be achieved by using the advanced toolkit which was not available on traditional analog hardware, as specified below:

  • The Reference Vernier allows easy alignment of 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 tools can compensate minor imperfection of analog tape player used for digitizing audio tapes.

  • The Play Trim is another tool for compensating weakened signal on aged pre-recorded tapes.

  • The EQ Converter offers digital translation between 120μs and 70μs IEC standards — 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.
All these fine-tuning tools can work independently from 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 allows the computer to perform as a outboard Dolby-B/C NR unit in one of the following four modes:

  • Audio-In to File (a digitizer/recorder).
  • File to Audio-Out (a player).
  • File to File (an off-line processor, with batch capability).
  • 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, no new Dolby-B/C hardware is in production today. In fact, vast majority of the analog Dolby-B/C units found today were produced decades ago and missing regular maintenance as required. They might drift out of the design 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 companding boxes.

It is possible to restore an aged Dolby-B/C hardware unit back to specification, which requires qualified service and knowledge. It is also worth noting that even a well calibrated hardware unit may not necessarily guarantee an accurate decoding of any Dolby-B/C pre-encoded audio because audio signal on a given tape might degrade over time or it was simply encoded by a drifted analog 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 the standard. A flexible decoder with adjustable parameters and fine-tuning tools may carry out better balanced result.

Interchangeability is another issue found between different Dolby-B/C enabled hardware devices that was largely overlooked. Audio content that was encoded by a Dolby-B/C hardware unit may not sounds perfect when being decoded by another Dolby-B/C units from different manufacturer/model/series. The fact can also be observed by comparing the factory data sheet closely against 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 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. Again, a flexible decoder may work better than a fixed decoder in this scenario.

DDi Codec is created as a digital alternative especially for those who are not fully confident/satisfied 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 designed with full respect to the original Dolby-B/C system topology and extensive study of the original analog schematics, combined with revers-engineering a few reputable analog Dolby-B/C hardware units. Dolby-B/C system has very unique non-linear characteristics of its own, which is not covered by the modern DSP theory in general. Attempting to simulate Dolby-B/C by customizing a linear EQ plugin is a simplistic, inaccurate and amateurish idea. DDi Codec takes innovative and proprietary approaches to overcome the unique challenges in order to digitally reproduce the non-linear sliding-band characteristics that are only found in Dolby-B/C system. The development was driven by science rather than subjective approximations.

The software will operate as a typical external (outboard) Dolby-B/C compatible compander with the convenient calibration options exposed to user, which offers better flexibility/potential to achieve optimal result. As a software solution, it is for the first time to allow Dolby-B/C decoding/encoding task being able to cross-benefit from the gifted digital advantages, such as: lossless fidelity, zero new noise, mathematical accuracy, wide dynamic range, low cost, no wear and no maintenance. The software 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 than using a real-time-only hardware. For studios/publishers, the software allows direct encoding the digital master copy and straightly feed it to a digital capable duplicating system, avoiding unnecessary analog processing, and perhaps, offering alternative licensing solution as well.

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 make the decision easier between the new software versus 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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