MuLaCover: Flexible Cover Song Generation via Symbolic Tonal Control
Organizations: MBZUAI · Peking University · MuLa Labs, Vera Praxis Lab · Nanjing University of the Arts ·
Abstract
A cover song re-renders an existing piece, most commonly by preserving its tonal content -- melody and chord progression -- while reshaping other musical attributes. This suggests a natural formulation for generative cover synthesis with pretrained music language models: explicitly control tonal content, while specifying lyrics and style through text. Existing approaches condition on frame-level features, tightly coupling generation to the reference's timing and structure, and limiting flexibility such as tempo variation, structural rearrangement, or partial conditioning. To this end, we present MuLaCover, a cover generation model that conditions a pretrained text-to-song foundation model on an editable symbolic lead sheet. Our design enables alignment-free control: generated outputs preserve the tonal signature of the source without frame-level alignment, allowing flexible timing, structure, and segment-level generation. We further introduce a training curriculum with partially mismatched audio-symbolic pairs, improving diversity and robustness. We evaluate MuLaCover with objective metrics, standard subjective ratings, and in-depth expert interviews that provide fine-grained diagnostic insights. Experiments show that MuLaCover achieves state-of-the-art performance among open-source systems and is competitive with leading commercial models such as Suno-v5.5. Audio samples and code are available at our project page: https://mulalabs.ai/mulacover/
Figures & tables
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| SongEcho [ 11 ] | 7.88 | 6.11 | 7.26 | 7.54 | 3.70 | 3.57 | 3.37 | 3.47 | 3.46 | 0.26 | 0.38 | 0.39 | 0.88 | 1.55 |
| ACE-Step-1.5 [ 12 ] | 8.29 | 6.30 | 7.68 | 7.86 | 4.48 | 4.46 | 4.26 | 4.35 | 4.36 | 0.21 | 0.30 | 0.40 | 0.95 | 1.10 |
| Suno-v5.5 [ 53 ] | 8.30 | 6.44 | 7.66 | 7.92 | 4.61 | 4.60 | 4.42 | 4.52 | 4.51 | 0.11 | 0.50 | 0.33 | 0.98 | 1.11 |
| MuLaCover | 8.34 | 6.34 | 7.70 | 7.93 | 4.59 | 4.59 | 4.34 | 4.44 | 4.47 | 0.13 | 0.41 | 0.48 | 0.97 | 1.05 |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| SongEcho [ 11 ] | 7.58 | 5.59 | 6.80 | 7.44 | 3.14 | 3.04 | 2.85 | 2.87 | 2.92 | 0.55 | 0.25 | 0.63 | 0.41 | 5.94 |
| ACE-Step-1.5 [ 12 ] | 8.26 | 5.91 | 7.66 | 7.84 | 4.22 | 4.20 | 3.95 | 4.08 | 4.08 | 0.36 | 0.34 | 0.50 | 0.52 | 4.92 |
| MuLaCover | 8.33 | 6.31 | 7.69 | 7.92 | 4.57 | 4.57 | 4.32 | 4.42 | 4.45 | 0.12 | 0.42 | 0.50 | 0.70 | 2.60 |
| Method | Identity Preserveness ( ) | Style Controllability ( ) | Creativeness ( ) | Overall Musicality ( ) |
|---|---|---|---|---|
| SongEcho [ 11 ] | ||||
| ACE-Step-1.5 [ 12 ] | ||||
| Suno-v5.5 [ 53 ] | ||||
| MuLaCover |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
| Variant | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| MuLaCover -small | 8.28 | 6.36 | 7.67 | 7.89 | 4.58 | 4.56 | 4.33 | 4.42 | 4.45 | 0.14 | 0.38 | 0.49 | 0.98 | 1.04 |
| Training schedule | ||||||||||||||
| w/o Warmup | 8.07 | 6.13 | 7.44 | 7.72 | 4.41 | 4.40 | 4.13 | 4.24 | 4.23 | 0.16 | 0.40 | 0.54 | 0.11 | 9.75 |
| w/ SP | 8.24 | 6.43 | 7.63 | 7.87 | 4.57 | 4.55 | 4.33 | 4.41 | 4.44 | 0.16 | 0.35 | 0.45 | 0.98 | 1.04 |
| Condition signal | ||||||||||||||
Appendix figures & tables15 assets
Supplementary material from the paper’s appendix.
Appendix
| Hyperparameter | Stage 1 | Stage 2 (w/o mask) | Stage 2 (w/ mask) | Stage 3 |
|---|---|---|---|---|
| Learning rate | ||||
| Epochs | 3 | 2 | 2 | 2 |
| Avg. bs/GPU | 9 | 1 | 1 | 1 |
| Trainable modules | GACA | GACA | GACA | GACA & LoRA |
| Trainable params | M | M | M | M |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| ACE-Step-1.5 | 8.25 | 5.58 | 7.64 | 7.80 | 4.21 | 4.17 | 3.93 | 4.08 | 4.07 | 0.37 | 0.39 | 0.56 | 0.08 | 12.40 |
| ACE-Step-1.5 | 8.23 | 5.87 | 7.64 | 7.78 | 4.28 | 4.25 | 4.03 | 4.14 | 4.17 | 0.29 | 0.37 | 0.50 | 0.25 | 8.03 |
| ACE-Step-1.5 | 8.28 | 6.30 | 7.67 | 7.86 | 4.48 | 4.46 | 4.25 | 4.34 | 4.36 | 0.21 | 0.30 | 0.40 | 0.95 | 1.10 |
| ACE-Step-1.5 | 8.28 | 6.40 | 7.64 | 7.87 | 4.51 | 4.49 | 4.29 | 4.37 | 4.38 | 0.13 | 0.27 | 0.36 | 1.00 | 1.00 |
| ACE-Step-1.5 | 8.27 | 6.43 | 7.61 | 7.86 | 4.51 | 4.50 | 4.29 | 4.38 | 4.38 | 0.11 | 0.27 | 0.34 | 1.00 | 1.00 |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| SongEcho [ 11 ] | 7.49 | 5.44 | 6.63 | 7.43 | 3.06 | 2.98 | 2.76 | 2.77 | 2.83 | 0.64 | 0.19 | 0.70 | 0.25 | 7.59 |
| ACE-Step-1.5 [ 12 ] | 8.26 | 5.86 | 7.65 | 7.83 | 4.19 | 4.17 | 3.91 | 4.05 | 4.04 | 0.36 | 0.35 | 0.51 | 0.38 | 6.18 |
| MuLaCover | 8.33 | 6.33 | 7.71 | 7.93 | 4.59 | 4.59 | 4.33 | 4.44 | 4.47 | 0.11 | 0.42 | 0.51 | 0.63 | 3.15 |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| SongEcho [ 11 ] | 7.41 | 5.43 | 6.56 | 7.32 | 2.87 | 2.76 | 2.63 | 2.58 | 2.67 | 0.64 | 0.20 | 0.72 | 0.25 | 7.61 |
| ACE-Step-1.5 [ 12 ] | 8.23 | 5.71 | 7.62 | 7.82 | 4.17 | 4.13 | 3.89 | 4.02 | 4.01 | 0.40 | 0.36 | 0.53 | 0.38 | 6.89 |
| MuLaCover | 8.31 | 6.27 | 7.66 | 7.91 | 4.54 | 4.54 | 4.29 | 4.39 | 4.43 | 0.12 | 0.42 | 0.51 | 0.55 | 3.36 |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| SongEcho [ 11 ] | 7.83 | 5.90 | 7.20 | 7.56 | 3.50 | 3.37 | 3.17 | 3.27 | 3.24 | 0.38 | 0.35 | 0.46 | 0.73 | 2.62 |
| ACE-Step-1.5 [ 12 ] | 8.30 | 6.16 | 7.70 | 7.87 | 4.31 | 4.30 | 4.06 | 4.16 | 4.19 | 0.32 | 0.32 | 0.46 | 0.82 | 1.68 |
| MuLaCover | 8.34 | 6.33 | 7.70 | 7.93 | 4.58 | 4.58 | 4.33 | 4.43 | 4.46 | 0.13 | 0.41 | 0.49 | 0.93 | 1.28 |
| Background | Identity Preserveness | Style Controllability | Creativeness | Overall Musicality | |
|---|---|---|---|---|---|
| Amateur | |||||
| Intermediate | |||||
| Professional |
| Metric | -value | Kendall’s | ||
|---|---|---|---|---|
| Identity Preserveness | ||||
| Style Controllability | ||||
| Creativeness | ||||
| Overall Musicality |
| Pair | Identity | Style | Creativeness | Overall |
|---|---|---|---|---|
| ACE-Step-1.5 vs. MuLaCover | ||||
| ACE-Step-1.5 vs. SongEcho | ||||
| ACE-Step-1.5 vs. Suno-v5.5 | ||||
| MuLaCover vs. SongEcho | ||||
| MuLaCover vs. Suno-v5.5 | ||||
| SongEcho vs. Suno-v5.5 |
| Attribute | Expert definition / judging criterion |
|---|---|
| Rhythm and groove | The most salient property of rhythm-and-blues: drums and bass jointly form the groove, and faithful R&B should exhibit typical rhythmic patterns rather than a generic pop or electronic feel. |
| Vocal melody, repetition, and variation | In R&B, melodic development often happens through modular repetition and varied repetition over a cyclic rhythmic/harmonic frame; phrase-end ornaments, melismas, and vocal timbre are important cues. |
| Version / system | Rhythm and groove | Vocal melody / timbre | Overall comment |
|---|---|---|---|
| A / ACE-Step-1.5 | : Electric drums, 808, and synthetic bass make the version sound closer to electronic pop. | : The vocal line is closer to a normal pop-song melody than to R&B melodic development. | The first two attributes deviate substantially from typical R&B; the version leans toward electronic pop rather than canonical R&B. |
| B / SongEcho | : The drum timbre and groove contain pop-R&B characteristics. | : The vocal development is closer to R&B: it uses a four-phrase loop rather than the linear emotional buildup typical of pop ballads. | Overall, this version is relatively better than Version A. |
| C / MuLaCover | : The expert rated the rhythm and groove higher than Versions A and B. | : The expert rated the vocal melodic treatment higher than Versions A and B; the verse also has a vocal timbre that sounds very R&B-like. | The expert judged it close to Version B in broad style but with a more R&B-like singer timbre; it is still not the most canonical R&B rendition. |
| D / Suno-v5.5 | : The groove is slightly better than the preceding versions. | : The vocal line is much more natural and close to pop R&B, especially in phrase endings, melismas, and timbre. | The expert also noted that the auxiliary harmonic and instrumentation-related attributes were relatively well matched. |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) |
| SongEcho [ 11 ] | 7.66 | 6.26 | 7.06 | 7.32 | 3.47 | 3.23 | 3.13 | 3.19 | 3.27 | 0.42 | 0.32 | 0.43 | 0.97 | 1.03 |
| ACE-Step-1.5 [ 12 ] | 8.27 | 6.08 | 7.67 | 7.86 | 4.37 | 4.36 | 4.15 | 4.25 | 4.25 | 0.25 | 0.31 | 0.31 | 0.98 | 1.08 |
| MuLaCover | 8.34 | 6.24 | 7.73 | 7.92 | 4.52 | 4.51 | 4.27 | 4.37 | 4.40 | 0.12 | 0.40 | 0.45 | 0.98 | 1.02 |
| AudioBox [ 54 ] ( ) | SongEval [ 55 ] ( ) | Lyrics | Style | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Method | PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) |
| HeartMuLa [ 10 ] | 8.23 | 6.32 | 7.61 | 7.89 | 4.68 | 4.69 | 4.51 | 4.58 | 4.60 | 0.15 | 0.27 | 0.59 |
| MuLaCover -nc | 8.30 | 6.18 | 7.68 | 7.92 | 4.60 | 4.59 | 4.34 | 4.43 | 4.47 | 0.11 | 0.41 | 0.59 |
| Corruption | AudioBox ( ) | SongEval ( ) | Lyrics | Style | CSI judge | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PQ | PC | CE | CU | Coh. | Mem. | Nat. | Cla. | Mus. | PER ( ) | MuQ-Sim ( ) | MuQ-Dist ( ) | CSI-R@1 ( ) | CSI-Rank ( ) | ||
| 0 | 0 | 8.34 | 6.34 | 7.70 | 7.93 | 4.59 | 4.59 | 4.34 | 4.44 | 4.47 | 0.13 | 0.41 | 0.48 | 0.97 | 1.05 |
| 0 | 5% | 8.29 | 6.26 | 7.67 | 7.90 | 4.54 | 4.52 | 4.25 | 4.35 | 4.40 | 0.13 | 0.40 | 0.56 | 0.63 | 2.85 |
| 0 | 10% | 8.26 | 6.22 | 7.61 | 7.87 | 4.48 | 4.46 | 4.18 | 4.29 | 4.34 | 0.14 | 0.40 | 0.57 | 0.42 | 5.10 |
| 5% | 0 | 8.26 | 6.20 | 7.61 | 7.89 | 4.51 | 4.50 | 4.23 | 4.32 | 4.37 | 0.13 | 0.39 | 0.56 | 0.62 | 2.91 |
| 10% | 0 | 8.29 | 6.26 | 7.70 | 7.91 | 4.57 | 4.56 | 4.28 | 4.39 | 4.44 | 0.11 | 0.38 | 0.57 | 0.44 | 3.69 |
| Lead sheet | ||
|---|---|---|
| Method | MS ( ) | CS ( ) |
| SongEcho [ 11 ] | 0.77 | 0.74 |
| ACE-Step-1.5 [ 12 ] | 0.63 | 0.86 |
| Suno-v5.5 [ 53 ] | 0.57 | 0.82 |
| MuLaCover | 0.68 | 0.89 |
Music Generation
Music generation studies computational methods for composing, synthesizing, and editing music from symbolic, audio, textual, and multimodal inputs.
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