---
license: mit
pipeline_tag: audio-to-audio
tags:
- audio-separation
- vocal-remover
- stem-separation
- onnx
- onnxruntime
---

# AudioSeparatorONNX

Collection of popular audio separation and vocal removal models converted to **ONNX** format, optimized for high-performance CPU/GPU inference using `onnxruntime`.

## 📌 Overview

This repository provides pre-converted ONNX versions of popular music source separation (MSS) and vocal removal models (such as UVR5 / Ultimate Vocal Remover models, MDX-Net, VR Architecture, Demucs, etc.). 

Using ONNX models allows for:
- **Cross-platform compatibility** (Python, C++, C#, Rust, JS, etc.).
- **Faster execution** with `onnxruntime` using CPU, CUDA, DirectML, CoreML, or TensorRT.
- **Lightweight deployments** without requiring heavy frameworks like PyTorch or TensorFlow in production.

---

## 💻 Quickstart

## 📦 Embedded Metadata (`sep_meta`)

Every `.onnx` file in this repository is **self-contained** — no separate sidecar `.json` file is needed. All inference parameters are embedded directly inside the ONNX model as a `metadata_props` entry with key `sep_meta`.

### Reading metadata with Python (`onnxruntime`)

```python
import json
import onnxruntime as ort

sess = ort.InferenceSession("Reverb_HQ_By_FoxJoy.onnx", providers=["CPUExecutionProvider"])
meta_map = sess.get_modelmeta().custom_metadata_map   # dict[str, str]
sep_meta = json.loads(meta_map["sep_meta"])

print(sep_meta["arch"])           # "MDX" | "VR" | "ROFORMER"
print(sep_meta["primary_stem"])   # "No Reverb"
print(sep_meta["secondary_stem"]) # "Reverb"
```

### Reading metadata with Python (`onnx` library, no ORT session)

```python
import json
import onnx

model = onnx.load("UVR-MDX-NET-Inst_HQ_1.onnx")
meta_map = {p.key: p.value for p in model.metadata_props}
sep_meta = json.loads(meta_map["sep_meta"])
```

### Reading metadata with C (fast byte-scan, no ORT dependency)

The `sep_meta` key is stored near the **end** of the ONNX protobuf binary, after all weight initializers. You can extract it with a simple byte scan — no need to load the entire model into memory:

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Returns a heap-allocated JSON string, or NULL on failure.
   Caller must free() the result. */
char* read_onnx_sep_meta(const char* onnx_path) {
    FILE* f = fopen(onnx_path, "rb");
    if (!f) return NULL;

    /* Read the last 64 KB — sep_meta is always at the end */
    const size_t SCAN_SIZE = 64 * 1024;
    fseek(f, 0, SEEK_END);
    long file_size = ftell(f);
    size_t read_size = (file_size < (long)SCAN_SIZE) ? (size_t)file_size : SCAN_SIZE;
    long offset = file_size - (long)read_size;
    fseek(f, offset, SEEK_SET);

    char* buf = (char*)malloc(read_size + 1);
    if (!buf) { fclose(f); return NULL; }
    size_t n = fread(buf, 1, read_size, f);
    fclose(f);
    buf[n] = '\0';

    /* Find the marker string "sep_meta" */
    const char* marker = "sep_meta";
    char* pos = buf;
    char* found = NULL;
    while ((pos = (char*)memchr(pos, 's', buf + n - pos)) != NULL) {
        if ((size_t)(buf + n - pos) >= strlen(marker) &&
            memcmp(pos, marker, strlen(marker)) == 0) {
            found = pos;  /* keep the last occurrence */
        }
        pos++;
    }
    if (!found) { free(buf); return NULL; }

    /* After "sep_meta" the protobuf stores the value string.
       Skip past the key and any protobuf length bytes until '{' */
    char* json_start = found + strlen(marker);
    while (json_start < buf + n && *json_start != '{') json_start++;
    if (json_start >= buf + n) { free(buf); return NULL; }

    /* Find matching closing '}' */
    int depth = 0;
    char* p = json_start;
    while (p < buf + n) {
        if (*p == '{') depth++;
        else if (*p == '}') { depth--; if (depth == 0) break; }
        p++;
    }
    if (depth != 0) { free(buf); return NULL; }

    size_t json_len = (size_t)(p - json_start) + 1;
    char* result = (char*)malloc(json_len + 1);
    memcpy(result, json_start, json_len);
    result[json_len] = '\0';

    free(buf);
    return result;
}

/* Example usage */
int main(void) {
    char* meta = read_onnx_sep_meta("Reverb_HQ_By_FoxJoy.onnx");
    if (meta) {
        printf("%s\n", meta);
        free(meta);
    }
    return 0;
}
```

---

## 🔬 `sep_meta` JSON Schema

The `sep_meta` value is a compact JSON object. Fields differ by architecture:

### MDX-Net models

```json
{
  "arch":           "MDX",
  "primary_stem":   "Vocals",
  "secondary_stem": "Instrumental",
  "sample_rate":    44100,
  "n_fft":          7680,
  "hop_length":     1024,
  "dim_f":          3072,
  "dim_t":          256,
  "compensate":     1.021,
  "overlap":        0.25
}
```

| Field | Type | Description |
|-------|------|-------------|
| `n_fft` | int | STFT window size |
| `hop_length` | int | STFT hop length |
| `dim_f` | int | Frequency bins fed to the network |
| `dim_t` | int | Time frames per chunk |
| `compensate` | float | Amplitude gain applied after iSTFT |
| `overlap` | float | Overlap ratio between consecutive chunks (0–0.75) |

**ONNX I/O:**
- Input: `input` — shape `(1, 4, dim_f, dim_t)` — four channels: `[real_L, imag_L, real_R, imag_R]`
- Output: `output` — same shape as input

### VR Architecture models

```json
{
  "arch":           "VR",
  "primary_stem":   "No Reverb",
  "secondary_stem": "Reverb",
  "sample_rate":    44100,
  "vr_model_param": "4band_v3",
  "bins":           672,
  "window_size":    512,
  "is_vr51":        true,
  "nn_arch_size":   218,
  "model_capacity": [32, 128],
  "band_params": {
    "1": {"sr": 11025, "n_fft": 2048, "trim": 0, "window": "hann", "agg": 10},
    "2": {"sr": 22050, "n_fft": 2048, "trim": 48, "window": "hann", "agg": 10},
    "3": {"sr": 44100, "n_fft": 2048, "trim": 48, "window": "hann", "agg": 10},
    "4": {"sr": 44100, "n_fft": 8192, "trim": 0, "window": "hann", "agg": 10}
  }
}
```

| Field | Type | Description |
|-------|------|-------------|
| `vr_model_param` | string | Band config preset name |
| `bins` | int | Total frequency bins after multi-band STFT |
| `window_size` | int | Window size for the primary STFT pass |
| `is_vr51` | bool | `true` = CascadedNet (UVR v5.1), `false` = v4 |
| `nn_arch_size` | int | Network depth parameter |
| `band_params` | object | Per-band STFT config used to build the input spectrogram |

**ONNX I/O:**
- Input: `input` — shape `(batch, 2, bins, frames)` — stereo multi-band magnitude spectrogram
- Output: `output` — shape `(batch, 2, bins, frames)` — predicted source mask

### Roformer models (MelBandRoformer / BSRoformer)

> **Note:** Roformer ONNX exports contain only the **transformer core**. STFT and iSTFT are not part of the ONNX graph (complex ops are not exportable). The inference wrapper must perform STFT → band-split → ONNX → scatter → iSTFT around the model.

```json
{
  "arch":               "ROFORMER",
  "roformer_type":      "MelBandRoformer",
  "primary_stem":       "No Reverb",
  "secondary_stem":     "Reverb",
  "sample_rate":        44100,
  "chunk_size":         264600,
  "hop_length":         1024,
  "n_fft":              2048,
  "dim_t":              256,
  "num_bands":          64,
  "dim":                128,
  "frames":             256,
  "n_freq_indices":     384,
  "num_bins":           1025,
  "n_full_freqs":       1025,
  "overlap":            2,
  "freq_indices":       [...],
  "num_bands_per_freq": [...]
}
```

| Field | Type | Description |
|-------|------|-------------|
| `chunk_size` | int | Audio samples per inference chunk |
| `hop_length` / `n_fft` | int | STFT params applied **outside** the ONNX graph |
| `num_bands` | int | Number of mel bands |
| `frames` | int | Time frames (= `dim_t`) |
| `n_freq_indices` | int | Number of selected frequency bins after mel gather |
| `freq_indices` | int[] | Frequency bin indices to gather from full STFT before passing to network |
| `num_bands_per_freq` | int[] | Band assignment per frequency bin (for scatter-add in iSTFT) |
| `overlap` | int | Number of overlapping inference passes per chunk |

**ONNX I/O:**
- Input: `x_bands` — shape `(1, frames, num_bands, dim)` — band-split STFT features
- Output: `masks` — shape `(1, 1, n_freq_indices, frames, 2)` — complex mask

---

## 🚀 Quickstart with `audio-separator`

The recommended way to run these models is [`audio-separator`](https://github.com/nomadkaraoke/python-audio-separator) — the same inference engine that powers [Ultimate Vocal Remover](https://github.com/Anjok07/ultimatevocalremovergui).

All `.onnx` and `.pth` files in this repo are fully compatible with `audio-separator` out of the box.

### Installation

```bash
# CPU only (macOS / Linux / Windows)
pip install "audio-separator[cpu]"

# Nvidia GPU (CUDA)
pip install "audio-separator[gpu]"

# Apple Silicon (CoreML acceleration)
pip install "audio-separator[cpu]"   # CoreML is auto-detected on macOS
```

### CLI usage

Download the model file from the **Files and versions** tab, then point `--model_file_dir` at the folder containing it:

```bash
# Remove reverb from a mix
audio-separator mix.wav \
  --model_filename Reverb_HQ_By_FoxJoy.onnx \
  --model_file_dir /path/to/downloaded/models \
  --output_dir ./output \
  --output_format WAV

# Vocal / instrumental separation
audio-separator mix.wav \
  --model_filename UVR-MDX-NET-Inst_HQ_3.onnx \
  --model_file_dir /path/to/downloaded/models \
  --output_dir ./output
```

### Python API

```python
from audio_separator.separator import Separator

separator = Separator(
    model_file_dir="/path/to/downloaded/models",  # folder with the .onnx files
    output_dir="./output",
    output_format="WAV",
)

# Load and run — arch is auto-detected from the file extension
separator.load_model("Reverb_HQ_By_FoxJoy.onnx")
output_files = separator.separate("mix.wav")
print("Output:", output_files)
```

### Adjusting inference parameters

`audio-separator` exposes the most important per-arch parameters:

```python
# MDX — tune overlap and segment size
separator = Separator(
    model_file_dir="/path/to/downloaded/models",
    mdx_params={
        "hop_length":    1024,
        "segment_size":  256,    # dim_t from sep_meta
        "overlap":       0.25,   # matches sep_meta default
        "batch_size":    1,
        "enable_denoise": False,
    }
)

# VR — tune aggression and window size
separator = Separator(
    model_file_dir="/path/to/downloaded/models",
    vr_params={
        "batch_size":    1,
        "window_size":   512,    # 320 = slower but better
        "aggression":    5,      # 0-100, higher = more aggressive separation
        "enable_tta":    False,
        "high_end_process": False,
    }
)

separator.load_model("UVR-DeEcho-DeReverb.onnx")
output_files = separator.separate("mix.wav")
```

> **Note on `sep_meta`:** `audio-separator` reads model parameters from its own internal `mdx_model_data.json` lookup table — it does **not** read the embedded `sep_meta` metadata. The `sep_meta` field is provided for custom inference pipelines and other runtimes (see sections below). embed_sep_meta(onnx_path: str, meta: dict) -> None:
```python
    model = onnx.load(onnx_path)
    # Remove stale entry if present
    existing = [p for p in model.metadata_props if p.key != "sep_meta"]
    del model.metadata_props[:]
    model.metadata_props.extend(existing)
    # Add new entry
    entry = model.metadata_props.add()
    entry.key   = "sep_meta"
    entry.value = json.dumps(meta, separators=(",", ":"))
    onnx.save_model(model, onnx_path)
```
# Example — MDX model

```python
embed_sep_meta("my_model.onnx", {
    "arch":           "MDX",
    "primary_stem":   "Vocals",
    "secondary_stem": "Instrumental",
    "sample_rate":    44100,
    "n_fft":          7680,
    "hop_length":     1024,
    "dim_f":          3072,
    "dim_t":          256,
    "compensate":     1.021,
    "overlap":        0.25,
})
```
---

## 📋 Requirements

```
onnxruntime >= 1.16
numpy >= 1.24
soundfile >= 0.12
```

For metadata-only access (no inference):
```
onnx >= 1.14
```

## 📄 License

The repository structure and conversion scripts are licensed under the [MIT License](https://www.google.com/search?q=LICENSE).
*Please check the original model licenses before using them for commercial purposes.*

---

## 🙏 Acknowledgments & Credits

Special thanks to the authors and maintainers of:

* [Ultimate Vocal Remover (UVR5)](https://www.google.com/search?q=https://github.com/Anemone95/Ultimate-Vocal-Remover-GUI)
* [audio-separator](https://www.google.com/search?q=https://github.com/beverlis/audio-separator)
* [ONNX Runtime](https://onnxruntime.ai/)