# A DNN Based Post-Filter to Enhance the Quality of Coded Speech in MDCT Domain

arXiv: https://arxiv.org/abs/2201.12039 · HTML: https://mlsanity.com/paper/2201.12039/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- Builds on 4 of its 21 references that are in the map.
- First posted on arXiv 28 Jan 2022.

## Builds on (most cited first, 4 of 4)

- [Adam: A Method for Stochastic Optimization](https://mlsanity.com/paper/1412.6980/) (2014)
- [Audio Codec Enhancement with Generative Adversarial Networks](https://mlsanity.com/paper/2001.09653/) (2020)
- [Improving Opus Low Bit Rate Quality with Neural Speech Synthesis](https://mlsanity.com/paper/1905.04628/) (2019)
- [Enhancement Of Coded Speech Using a Mask-Based Post-Filter](https://mlsanity.com/paper/2010.05571/) (2020)

## Built on by (most cited first, 1 of 1)

- [Neural Spectral Band Generation for Audio Coding](https://mlsanity.com/paper/2506.06732/) (2025)

## Abstract (arXiv)

Frequency domain processing, and in particular the use of Modified Discrete Cosine Transform (MDCT), is the most widespread approach to audio coding. However, at low bitrates, audio quality, especially for speech, degrades drastically due to the lack of available bits to directly code the transform coefficients. Traditionally, post-filtering has been used to mitigate artefacts in the coded speech by exploiting a-priori information of the source and extra transmitted parameters. Recently, data-driven post-filters have shown better results, but at the cost of significant additional complexity and delay. In this work, we propose a mask-based post-filter operating directly in MDCT domain of the codec, inducing no extra delay. The real-valued mask is applied to the quantized MDCT coefficients and is estimated from a relatively lightweight convolutional encoder-decoder network. Our solution is tested on the recently standardized low-delay, low-complexity codec (LC3) at lowest possible bitrate of 16 kbps. Objective and subjective assessments clearly show the advantage of this approach over the conventional post-filter, with an average improvement of 10 MUSHRA points over the LC3 coded speech.