**Multi-band MelGAN**, or **MB-MelGAN**, is a waveform generation model focusing on high-quality text-to-speech. It improves the original [MelGAN](https://paperswithcode.com/method/melgan) in several ways. First, it increases the receptive field of the generator, which is proven to be beneficial to speech generation. Second, it substitutes the feature matching loss with the multi-resolution STFT loss to better measure the difference between fake and real speech. Lastly, [MelGAN](https://paperswithcode.com/method/melgan) is extended with multi-band processing: the generator takes mel-spectrograms as input and produces sub-band signals which are subsequently summed back to full-band signals as discriminator input.

**Attention-augmented Convolution** is a type of [convolution](https://paperswithcode.com/method/convolution) with a two-dimensional relative self-attention mechanism that can replace convolutions as a stand-alone computational primitive for image classification. It employs [scaled-dot product attention](https://paperswithcode.com/method/scaled) and [multi-head attention](https://paperswithcode.com/method/multi-head-attention) as with [Transformers](https://paperswithcode.com/method/transformer).

It works by concatenating convolutional and attentional feature map. To see this, consider an original convolution operator with kernel size $k$, $F\_{in}$ input filters and $F\_{out}$ output filters. The corresponding attention augmented convolution can be written as"

$$\text{AAConv}\left(X\right) = \text{Concat}\left[\text{Conv}(X), \text{MHA}(X)\right] $$

$X$ originates from an input tensor of shape $\left(H, W, F\_{in}\right)$. This is flattened to become $X \in \mathbb{R}^{HW \times F\_{in}}$ which is passed into a multi-head attention module, as well as a convolution (see above).

Similarly to the convolution, the attention augmented convolution 1) is equivariant to translation and 2) can readily operate on inputs of different spatial dimensions.

Attention-augmented Convolution

Attention Augmented Convolutional Networks

Multi-band MelGAN

Multi-band MelGAN: Faster Waveform Generation for High-Quality Text-to-Speech

**Mixture Normalization** is normalization technique that relies on an approximation of the probability density function of the internal representations. Any continuous distribution can be approximated with arbitrary precision using a Gaussian Mixture Model (GMM). Hence, instead of computing one set of statistical measures from the entire population (of instances in the mini-batch) as [Batch Normalization](https://paperswithcode.com/method/batch-normalization) does, Mixture Normalization works on sub-populations which can be identified by disentangling modes of the distribution, estimated via GMM. 

While BN can only scale and/or shift the whole underlying probability density function, mixture normalization operates like a soft piecewise normalizing transform, capable of completely re-structuring the data distribution by independently scaling and/or shifting individual modes of distribution.

Source	Multi-band MelGAN: Faster Waveform Generation for High-Quality Text-to-Speech
Year	2000
Data Source	CC BY-SA - https://paperswithcode.com