In recent years, neural vocoders have surpassed classical speech generation approaches in naturalness and perceptual quality of the synthesized speech. Computationally heavy models like WaveNet and WaveGlow achieve best results, while lightweight GAN models, e.g. MelGAN and Parallel WaveGAN, remain inferior in terms of perceptual quality. We therefore propose StyleMelGAN, a lightweight neural vocoder allowing synthesis of high-fidelity speech with low computational complexity. StyleMelGAN employs temporal adaptive normalization to style a low-dimensional noise vector with the acoustic features of the target speech. For efficient training, multiple random-window discriminators adversarially evaluate the speech signal analyzed by a filter bank, with regularization provided by a multi-scale spectral reconstruction loss. The highly parallelizable speech generation is several times faster than real-time on CPUs and GPUs. MUSHRA and P.800 listening tests show that StyleMelGAN outperforms prior neural vocoders in copy-synthesis and Text-to-Speech scenarios.
This paper is about geometric and Riemannian properties of Engel structures. A choice of defining forms for an Engel structure $\mathcal{D}$ determines a distribution $\mathcal{R}$ transverse to $\mathcal{D}$ called the Reeb distribution. We study conditions that ensure integrability of $\mathcal{R}$. For example, if we have a metric $g$ that makes the splitting $TM=\mathcal{D}\oplus \mathcal{R}$ orthogonal and such that $\mathcal{D}$ is totally geodesic then there exists another Reeb distribution, which is integrable. We introduce the notion of K-Engel structures in analogy with K-contact structures, and we classify the topology of K-Engel manifolds. As natural consequences of these methods, we provide a construction that is the analogue of the Boothby–Wang construction in the contact setting, and we give a notion of contact filling for an Engel structure.
This paper is about geometric and Riemannian properties of Engel structures, i.e. maximally non-integrable 2-plane fields on 4-manifolds. Two 1-forms α and β are called Engel defining forms if D = ker α ∩ ker β is an Engel structure and E = ker α is its associated even contact structure, i.e. E = [D, D]. A choice of Engel defining forms determines a distribution R transverse to D called the Reeb distribution. We study conditions that ensure integrability of R. For example if we have a metric g which makes the splitting T M = D ⊕ R orthogonal and such that D is totally geodesic then there exists an integrable Reeb distribution R.It turns out that integrabilty of R is related to the existence of vector fields Z whose flow preserves D, so called Engel vector fields. A K-Engel structure is a triple (D, g, Z) where D is an Engel structure, g is a Riemannian metric, and Z is a vector field which is Engel, Killing, and orthogonal to E . In this case we can construct Engel defining forms with very nice properties and such that R is integrable. Moreover we can classify the topology of K-Engel manifolds studying the action of the flow of Z. As natural consequences of these methods we provide a construction which is the analogue of the Boothby-Wang construction in the contact setting and we give a notion of contact filling for an Engel structure.
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