ADC (Adaptive Differential Coding) . Lossy Audio Codec and more.

Advanced Domain Compressor

(ADC)

Redefining Time-Domain Audio Compression

ADC is a next-generation audio codec engineered to achieve exceptional compression efficiency and perceptual quality by fundamentally challenging the conventional reliance on frequency-domain processing. As an advanced evolution of time-domain compression, ADC introduces a sophisticated 8-band filter bank architecture combined with state-of-the-art entropy coding, delivering a massive leap in performance and coding gain.

Key Features & Technical Deep Dive

Core Architecture: The Time-Domain Advantage Unlike codecs that map the entire signal to the frequency domain (e.g., MDCT-based codecs), ADC operates directly on the raw audio waveform, capitalizing on temporal correlation for extreme efficiency. This approach results in ultra-low latency and total immunity to the temporal artifacts and pre-echo often associated with block-based transforms.

Eight-Band Filter Bank Processing The latest iteration of ADC employs a highly optimized eight-band filter bank to decompose the input signal, doubling the granularity of previous versions.

1.  High-Granularity Waveform Division: The incoming audio waveform is precisely split into eight distinct subbands, allowing for a much finer spectral analysis while staying within the time domain.

2.  Enhanced Perceptual Isolation: Each of the eight subbands is processed independently. This increased resolution allows the compressor to apply even more surgical, high-resolution processing to specific frequency ranges, drastically optimizing the noise floor distribution and efficiency.

Advanced Contextual Coding The primary compression gain is achieved within these subbands using a refined, predictive entropy method:

• Contextual Time-Domain Compression: Each subband's waveform is compressed using an Advanced Contextual Coding scheme. This algorithm exploits deep statistical dependencies between successive samples and across the eight subbands, resulting in superior prediction accuracy and significantly reduced residual energy.
• High-Performance Range Coding: The final stage utilizes an evolved Range Coding engine to represent the predictive residuals. This powerful entropy encoder achieves near-optimal compression ratios, making ADC exceptionally efficient even at extremely low bitrates.

A New Era of Audio Quality

Quality Over Perfect Reconstruction While earlier versions focused on Perfect Reconstruction (PR), ADC decisively prioritizes perceptual optimization. By strategically trading the strict mathematical PR property for advanced noise shaping and psychoacoustic efficiency, ADC achieves a massive improvement in perceived audio transparency.

Performance Benchmark ADC is engineered for a modern landscape where efficiency and quality are paramount:

• Next-Gen Efficiency: Thanks to the new 8-band architecture, ADC's efficiency has been significantly boosted, often surpassing established frequency-domain codecs (e.g., LC3, AAC) in both bitrate-to-quality ratio and computational overhead.
• Superior Transient Fidelity: By leveraging the high-resolution 8-band filter bank, ADC exhibits inherent strengths in preserving lightning-fast transients, delivering a crispness and "air" that transform-based codecs often struggle to maintain.
• Native Joint Stereo Support: Optimized for spatial efficiency and modern stereo imaging.

Flexible Rate Control: VBR vs. CBR

ADC provides versatile encoding modes to suit different transmission and storage requirements, with a clear focus on maximizing data economy:

·       Optimal VBR (Variable Bitrate): This is the native and most efficient mode for ADC. By dynamically allocating bits based on the instantaneous complexity of the 8 subbands, the VBR engine ensures a consistent perceptual quality while minimizing the overall file size. It is the recommended mode for achieving the highest efficiency gains.

·       Standard CBR (Constant Bitrate): For applications requiring fixed bandwidth, ADC supports CBR encoding. While highly reliable for streaming, this mode is inherently less efficient than VBR, as it lacks the fluid adaptability to the signal's varying entropy.

USAGE:

  Compression:   adc c [options] <input.wav> <output.adc>
  Decompression: adc d <input.adc> <output.wav>
  Play:          adc p <input.adc>

Options:
  -v<bitrate>  Set VBR birtare (64  - 320 kbps) default 128 kbps
  -b<bitrate>  Set CBR birtare (64  - 320 kbps)
  -j           Enable Joint Stereo

Example:
 adc c -v64  input.wav out.adc

adc c -b64  input.wav out.adc

adc d out.adc output.wav

home:  http://heartofcomp.altervista.org/ADCodec.htm

discussion: https://encode.su/threads/4291-ADC-(Adaptive-Differential-Coding)-My-Experimental-Lossy-Audio-Codec

contact mail: miadebora@homail.it