REVIEW 4 major objections 6 minor 33 references
Stereo sound event localization and detection based on PSELDnet pretraining and BiMamba sequence modeling
T0 review · 4 major / 6 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read By swapping the Conformer decoder for a bidirectional Mamba with asymmetric convolutions, this paper reports the best stereo SELD scores on the DCASE2025 Task 3 development set, using roughly a third of the Conformer's parameters.
desk verdict Plausible engineering tweak; the 'significantly better' claim is undercut by uncontrolled hyperparameters. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the BiMamba module: a bidirectional selective state-space model that processes a sequence forward and backward and fuses the hidden states, combined with asymmetric convolutions that alternate between the time and frequency dimensions. This decoder replaces the Conformer in the CNN14-Conformer PSELDnet. A second load-bearing step is the conversion of stereo left-right signals into pseudo first-order-ambisonic (FOA) channels, $W = (L+R)/2$ and $Y = (L-R)/2$ with $X = Z = 0$, which lets the pretrained FOA-based PSELDnet be fine-tuned on stereo data. The mechanism is meant to capture both directions of temporal context and to decouple time-frequency features, handling overlapping events better than the CRNN baseline.
What would settle it
Retrain the Conformer and BiMambaAC models under identical hyperparameters (same seed, learning rate, batch size, weight decay) or a small shared hyperparameter grid, and check whether BiMambaAC keeps its 1.4-point F1 lead over Conformer; a Conformer configuration that matches or exceeds 39.6% F1 would falsify the paper's central claim.
Extended reading notes
Core claim
On the paper's own terms, the discovery is that the CNN14-BiMamba hybrid — a pretrained CNN14 encoder with a BiMamba decoder plus asymmetric convolution — reaches a location-dependent F1 of 39.6%, a DOA error of 15.8°, and a relative distance error of 33% on the DCASE2025 Task 3 development set, with 76M parameters and 4.63G MACs. This beats the Conformer decoder (38.2% F1, 15.9° DOAE, 33% RDE, 210M parameters) and the CRNN baseline (22.8%, 24.5°, 41%, 0.7M), and is the best configuration the authors tested. The paper also claims that the asymmetric convolutions are responsible for part of the gain, since BiMamba without them scores 36.2% F1 with 178M parameters.
Load-bearing premise
The comparison assumes that the single training run per model, with different learning rates, batch sizes, and weight decay for each architecture, is a fair way to rank architectures; if those hyperparameters, rather than the BiMamba design, explain the score gap, the headline claim collapses.
Editorial extensions
If this is right
- If the result holds, BiMamba can serve as a drop-in Conformer replacement in pretrained SELD networks, cutting parameters by roughly a factor of three without losing accuracy.
- The pseudo-FOA reconstruction trick suggests that large FOA-pretrained models can be adapted to stereo-only consumer content rather than requiring new stereo pretraining.
- Asymmetric convolutions appear to be a cheap way to shave parameter count and improve discrimination of overlapping events, which may transfer to other time-frequency audio tasks.
- The reported 39.6% F1 on the development set provides a concrete reference point that future stereo SELD systems can compare against.
Reading between the lines
- The same decoder swap could transfer to other audio tasks that currently pair a pretrained encoder with an attention decoder, though the paper does not test this.
- Because the stereo-to-pseudo-FOA reconstruction discards the X and Z ambisonic components, an open question is whether a binaural or stereo-native pretraining objective would preserve spatial information that the current pipeline loses.
- The azimuth folding to [-90°, 90°] exploits the fixed frontal perspective of this year's challenge; an obvious extension is testing whether the architecture handles full 360° azimuth when labels are not folded.
- The channel-swap augmentation and pseudo-FOA trick could apply to other fixed-perspective SELD settings, such as smart displays or robotics, without collecting new spatial audio data.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a stereo sound event localization and detection (SELD) system for the DCASE2025 Task 3 audio-only track. The authors convert stereo input into a pseudo-FOA representation, fine-tune pretrained PSELDnet models, and replace the Conformer decoder in the CNN14-Conformer architecture with a bidirectional Mamba (BiMamba) module combined with asymmetric convolutions, calling the resulting model BiMambaAC. On the development set, BiMambaAC is reported to achieve an F1 score of 39.6%, DOAE of 15.8 degrees, and RDE of 33% with 76M parameters and 4.63G MACs, compared with 38.2%, 15.9 degrees, 33%, 210M parameters, and 4.69G MACs for the Conformer variant, and 22.8%, 24.5 degrees, and 41% for the official baseline. The paper concludes that BiMambaAC is significantly better than the Conformer decoder while reducing computational complexity.
Significance. If the reported comparison were robust, the paper would provide useful evidence that state-space decoders can replace Transformer decoders in a pretrained SELD pipeline with fewer parameters and comparable or better accuracy. The use of public challenge data, a standardized evaluation protocol, and reporting of parameter counts and MACs are strengths. However, the central architecture comparison currently rests on a single run per model with deliberately different training hyperparameters, so the headline claim of significant improvement is not yet supported. The incremental nature of the technical change and the absence of statistical significance testing limit the contribution to a suggestive empirical result rather than a definitive architecture comparison.
major comments (4)
- [Section 4 and Table 1] The central comparative claim that BiMambaAC outperforms the Conformer decoder is supported only by a single run per model with uncontrolled training hyperparameters. Section 4 reports different learning rates, weight decays, and batch sizes for each model (BiMambaAC: lr 3e-5, wd 5e-6, bs 32; Conformer: lr 1e-4, wd 1e-4, bs 256). With a fixed 120-epoch budget, the batch size difference alone gives BiMambaAC roughly eight times more parameter updates per epoch, so the 1.4-point F1 gap (39.6% vs. 38.2%) and 0.1-degree DOAE gap (15.8 degrees vs. 15.9 degrees) in Table 1 cannot be attributed to the BiMamba architecture. Please run multiple seeds and either match the training recipe across models or perform a hyperparameter sweep; without this, the abstract's 'significantly better' is unsupported.
- [Section 5 and Conclusion] The conclusion that BiMambaAC achieves 'the best overall performance across all metrics' is not consistent with Table 1: HTS-AT has a lower RDE (30% vs. 33%), and BiMambaAC's RDE is identical to that of Conformer and BiMamba. The advantage over Conformer is limited to F1 and DOAE, with DOAE differing by only 0.1 degree. Please revise the abstract and conclusion to state precisely which metrics are improved and by how much.
- [Section 5, Table 1] The 'reduced computational complexity' claim is overstated as written. Table 1 shows BiMambaAC at 4.63G MACs versus 4.69G for Conformer, a 1.3% reduction, while the parameter count drops from 210M to 76M. If the claim refers to parameter count, it should say so explicitly; if it refers to MACs, the difference is marginal and should not be described as a major advantage, especially since HTS-AT already operates at 2.88G MACs.
- [Section 3.3 and Section 4] The paper does not state whether the BiMamba module and the asymmetric convolution layers are initialized from pretrained weights or randomly initialized, whereas the Conformer decoder inherits PSELDnet pretrained weights. If the BiMamba components are randomly initialized, the comparison mixes initialization and architecture effects. Please disclose the initialization scheme and, ideally, train the Conformer baseline from the same random initialization to isolate the contribution of the architecture change.
minor comments (6)
- [Section 5, paragraph 2] The Conformer DOAE is reported as 16.6 degrees in the text but 15.9 degrees in Table 1; please correct and unify the value.
- [Section 3.1, Eq. (4)] Setting X(n)=Z(n)=0 discards all non-horizontal spatial information; please state explicitly that the pseudo-FOA representation is azimuth-only and discuss the implications for the evaluation, which already excludes elevation.
- [Section 4] The sentence 'the random seed is set to be 42' implies a single seed; please state the number of seeds used per configuration, consistent with the request for multiple runs in the major comments.
- [Throughout] The capitalization of PSELDnet/PSELDNet is inconsistent; please standardize the spelling.
- [Table 1] The baseline row is crowded ('Baseline0.7M57M'); please format the table for readability.
- [References] Several references are listed as arXiv preprints; where peer-reviewed versions now exist, please update the citation details.
Circularity Check
No circularity: the paper is an empirical comparison against an external benchmark, and the pretrained models are inputs rather than conclusions.
full rationale
The central claim is that fine-tuning PSELDnet-based models with a BiMamba decoder and asymmetric convolutions improves SELD performance on the DCASE2025 Task 3 development set relative to the challenge baseline and the original Conformer-decoder PSELDnet. This is an experimental evaluation, not a derivation. The pretrained PSELDnet weights are adopted from prior work and are used as starting points for fine-tuning, so citing them is a legitimate use of external building blocks, not a self-citation that supplies the conclusion. No quantity called a prediction is obtained by inverting a fitted parameter or by re-using the target metric as an input. The reported F1, DOAE, RDE, parameter counts, and MACs are measured on the development set's test split according to the challenge protocol. The use of different batch sizes, learning rates, and weight decay values across models is a potential experimental confound and a fairness concern, but it is not circular reasoning; it does not make any result true by definition. The paper's equations (SSM discretization, pseudo-FOA conversion, and activation functions) are standard technical components and none of them is defined in terms of the reported results. The only self-citations are incidental references to the authors' prior work on sound event detection and localization, and none of those citations is load-bearing for the paper's main comparison. Overall, no circular step is identifiable, so a score of 0 is appropriate.
Assumptions & free parameters
free parameters (1)
- Per-model training hyperparameters =
BiMambaAC: lr 3e-5, weight decay 5e-6, batch size 32; Conformer: lr 1e-4, wd 1e-4, bs 256; etc.
assumptions (3)
- domain assumption Stereo-to-pseudo-FOA conversion (W=(L+R)/2, Y=(L-R)/2, X=0, Z=0) retains sufficient spatial information for SELD.
- standard math Mamba state-space model discretization (Eqs. 1-3) is a valid basis for sequence modeling in this audio task.
- domain assumption Audio Channel Swapping (ACS) augmentation produces valid DOA label flips under the front-back ambiguity folding.
Cite this review
Pith. "Pith review of Stereo sound event localization and detection based on PSELDnet pretraining and BiMamba sequence modeling." pith.science (2026). https://pith.science/paper/Z3NSOYJQ
@misc{pith2026250613455,
author = {Pith},
title = {Pith review of: Stereo sound event localization and detection based on PSELDnet pretraining and BiMamba sequence modeling},
year = {2026},
howpublished = {\url{https://pith.science/paper/Z3NSOYJQ}},
note = {Machine review of arXiv:2506.13455}
}
read the original abstract
Pre-training methods have achieved significant performance improvements in sound event localization and detection (SELD) tasks, but existing Transformer-based models suffer from high computational complexity. In this work, we propose a stereo sound event localization and detection system based on pre-trained PSELDnet and bidirectional Mamba sequence modeling. We replace the Conformer module with a BiMamba module and introduce asymmetric convolutions to more effectively model the spatiotemporal relationships between time and frequency dimensions. Experimental results demonstrate that the proposed method achieves significantly better performance than the baseline and the original PSELDnet with Conformer decoder architecture on the DCASE2025 Task 3 development dataset, while also reducing computational complexity. These findings highlight the effectiveness of the BiMamba architecture in addressing the challenges of the SELD task.
Reference graph
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INTRODUCTION The objective of the sound event localization and detection (SELD) task is to identify sound events from predefined target classes, track their temporal dynamics, and estimate their respective spatial tra- jectories where they are active[1].This technology plays a vital role in various real-world applications, such as robotic auditory sensing...
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THEORY The Mamba architecture, based on the S4 (Structured State Space Sequence) model [25, 26], effectively combines the advantages of CNN and RNN, allowing the use of CNN’s parallel computation benefits during training and RNN’s temporal modeling capabilities during inference. The introduction of state-selection mechanisms allows the model to selectivel...
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PROPOSED METHOD 3.1. Feature Extraction Since PSELDNet operates on FOA-format audio data by concate- nating 4-channel log-mel spectrograms with 3-channel intensity vectors, to meet the input feature requirements of the pre-trained network, we convert the stereo left-right ear signalsL(n)andR(n) back to the FOA componentsW(n)andY(n)according to the ACN/SN3...
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The audio is resampled to 24 kHz, and 64 mel filters are used for feature extraction
TRAINING The proposed system is trained on the development dataset (stereo format) of STARSS23[27]. The audio is resampled to 24 kHz, and 64 mel filters are used for feature extraction. The short-time Fourier transform (STFT) is computed with a hop length of 20 ms (480 samples) and a window length of 40 ms. Each input feature consists of 250 frames, corre...
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RESULTS Table 1 presents a quantitative comparison between the baseline system and various pre-trained models on the development set. The metrics reported include the number of model parameters, the location-dependent F1-score (F 20◦, higher is better), the Direction of Arrival Error (DOAE, lower is better), and the Relative Distance Error (RDE, lower is ...
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CONCLUSION In this work, we propose a novel approach for stereo sound event lo- calization and detection (SELD) by combining PSELDnet pretrain- ing with BiMamba sequence modeling. Our experimental results demonstrate several key findings:First, the integration of pre-trained models significantly improves SELD performance compared to the Detection and Clas...
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Reviewed August 15, 2026 · model on record in the stance chip above.
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