Transcript swyx: Okay, welcome to Latent Space. We’re here in the studio with our gues co-host Vibh u. Welcome. Thanks. Excited for this one as well as Guillaume and Pavan from Mistral. Welcome. Excited to be here. Guillaume: Thank you. swyx: Pavan, you are leading audio research at Mistral and Guillaume, you're Chief Scientist, Announcing Voxtral TTS swyx Host Vibhu Host swyx Host Guillaume Guest swyx What’s the decision factor? Guillaume It’s a good question. swyx There will be more. Yeah, Pavan, any sort of research notes to add on? Architecture and Codec Pavan: But it’s a novel architecture that we develop inhouse. We traded on several internal architectures and ended up with a auto aggressive flow matching architecture. And also have a new in-house neural audio codec. Which, converts this audio into all point by herds latent [00:02:00] tokens, semantic and acoustic tokens. And yeah, that’s that’s their new part about this model and we’re pretty excited that it’s, it came out with such good quality and Jim was mentioning. Yeah, it’s a three B model. It’s based off of the TAL model that we actually released just a few months back and insert trunk and mainly meant for like the TTS stuff, but they need text capabilities are also there. Yeah. swyx: So there’s a lot to cover. I always I love any, anything to do with novel encodings and all those things because I think that’s obviously I creates a lot of efficiency, but also maybe bugs that sometimes happen. You were previously a Gemini and you worked on post training for language models, and maybe a lot of people will have less experience with audio models just in general compared to pure language. What did you find that you have to revisit from scratch as you joined this trial and started doing this? At least Understanding vs Generation Pavan: when it comes to, for, I think the, there are two buckets, I guess the audio understanding and audio [00:03:00] generation. The audio understanding, like the walkthrough models that Kim was mentioning that we released earlier. The walkthrough chat that we released I think July last year, and the follow up transcription only, models family that we released in January, that would be one bucket, and the generation is another bucket. I think. You can also treat them as a unified set of models, but currently the approaches are a little different between these two. To your question on how audio is fed to the model? In the understanding model, it’s very similar to actually Pixar models that we also released, swyx: yes. Pavan: That’s swyx: amazing. Pavan: It was pretty, I, that was the first project I worked on after joined Misra. It was pretty, pretty nice. And Wtu was very similar in spirit. I guess So we feed audio through an audio encoder similar to images through a vision encoder, and it produces continuous embeddings and which are fed as tokens to the main transformer decoded transformer model. Yeah. On the model output is just text. So on the output side, there is nothing that needs to be done in these kinds of mode. I [00:04:00] guess the interesting part of what the generation stuff is, the output now has to produce audio and. The approach that we have is this neural audio codec, which converts audio into these latent tokens. There is a lot of existing attrition and a lot of models which are based off of this kind of approach. And we took a slightly. A different, design decisions around this. But at the end of the day, the neural audio product converts audio into a 12.5 herdz set of latents. And each latent is, has a semantic token and a set of acoustic tokens. And the idea is that you take these discrete tokens and then feed it on the input side. There’s several ways to use this at each frame, but we just sum the embedding. So it’s like having key different vocabularies. Combine all of them because they all correspond to one audio frame on the input side. The output side is the interesting part on the output side, the, it’s not the, I don’t know if it’s the most popular, but one. Popular technique is to have a depth transformer [00:05:00] because you have K tokens at each time step, like with a text, you just have one token at each time step. So you just do predict the token from the vocabulary with, yeah, with just, you get probability swyx: This’s a very straightforward text. Very Pavan: straightforward. swyx: Yeah. Pavan: But if you have K tokens, then the name thing would be to predict all of them in paddle. That doesn’t work. At least that doesn’t work that well because audio has more entropy. And the, one of the techniques people use is this depth transformer where you you almost have a small transformer, or it can be L-S-T-M-R in as well, but people use transformers and you predict the K tokens in auto aggressive fashion in that. So you have two auto reive things going on. Flow Matching for Audio Pavan: So the thing we did differently is in, instead of having this auto aggressive K step prediction, we have a flow matching model. Instead of modeling this as a discrete token set we trained the codec to be both discrete and continuous to have this flexibility. So we did try the discrete stuff too, and which it works well, but the continuous stuff works just better. So yeah, we took this flow matching, so the, it’s a flow [00:06:00] matching head, which takes the latent from the main transformer and like kind in fusion, it’s denoising, but in this flow matching itself, velocity estimate. So you go from this noise t all the way to there. Audio latent, which corresponds to the 80 millisecond audio and then, which is sent through the work order to get back the 80 millisecond audio frame. swyx: Yeah. Is this the first application of flow matching in audio? Because usually I come across this in the image. Pavan: Yeah. Actually, in some sense there are models flow matching models in audio, but I think this specific combination I could be wrong. There could be somewhat. No. I haven’t seen. I haven’t seen much work in this, so I think it’s novel and a lot of it’s just a way bigger community, so they, I think they pioneer a lot of these diffusion flow matching work, and it’s interesting to adopt some of the ideas there into audio and, swyx: yeah. Pavan: Yeah, I’m, personally that’s the think part which is trying out about. One of more meta point is unlike text, even