Training Data Decides Quality: Lessons from a 690,517-Hour Vietnamese Speech Corpus

In the field of Artificial Intelligence, particularly speech recognition, there is a common misconception that algorithms are the sole deciding factor. In reality, the quality and scale of Vietnamese speech data are the strongest foundation for building an accurate model. This article analyzes practical lessons from AIVISION’s process of building and refining a corpus up to 690,517 hours, helping you understand why investing in data is more critical than simply optimizing code.

Why Data Matters More Than Algorithms?

When training an AI model, the algorithm acts as the "recipe," while data is the "ingredients." If the ingredients are flawed, inconsistent, or lack diversity, no matter how sophisticated the recipe is, the final product will be poor quality. For the Vietnamese language, the biggest challenge lies in the diversity of voices, dialects, and usage contexts.

A good speech recognition model must not only understand standard sample sentences but also handle environmental noise, regional dialects, and specifically the phenomenon of mixing English within Vietnamese sentences (code-switching). This is a point where many open-source multilingual models struggle when applied directly to the Vietnamese market without deep data refinement.

Lessons from AIVISION’s 690,517-Hour Corpus

AIVISION has spent years collecting and cleaning a massive data repository. The number 690,517 hours is not just a statistic; it is the result of a rigorous data processing pipeline. Here are the core elements that made the difference:

1. Diversity in Context and Dialects

Training data cannot come from a single source like news broadcasts or textbooks. We integrated data from various sources:

• Conferences and business meetings: Containing many specialized terms, fast speaking speeds, and multiple speakers interrupting each other.
• Everyday conversations: Reflecting natural communication, including slang, abbreviations, and Northern-Central-Southern dialects.
• Medical and legal data: Fields that require extremely high accuracy and contain many foreign terms.

This diversity helps the model learn a complete "map" of Vietnamese sounds, thereby minimizing errors when encountering complex real-world situations.

2. High-Quality Cleaning and Annotation Process

Having a lot of data is useless if it is "junk" data, as it will teach the model in the wrong direction. At AIVISION, we apply a multi-layered review process:

• Background noise removal: Using preprocessing techniques to separate speech from environmental noise.
• Accurate Transcription: Each audio clip is checked and rewritten word-for-word by Vietnamese language experts, including punctuation and sentence breaks.
• Code-switching handling: Data containing mixed English is clearly marked so the model can recognize and process it naturally.

3. Balancing Quantity and Quality

In the early stages, AIVISION focused on scaling up. However, when the corpus reached a sufficient size (hundreds of thousands of hours), the focus shifted to improving quality. We discovered that removing the lowest 10% of data quality from the 690,517-hour corpus significantly increased the overall accuracy of the model.

Impact on Speech-to-Text Accuracy

The result of serious investment in data is clearly reflected in measurement metrics. In internal benchmarks on held-out test sets, AIVISION’s model achieved an average Word Error Rate (WER) of 11.84%.

Our model achieves an average WER of 11.84%. This difference does not come from a "magic" algorithm, but from the model being "nourished" by high-quality Vietnamese data that matches real user contexts.

The table below illustrates performance on different datasets:

Test Dataset	AIVISION WER	Notes
FLEURS-vi	4.58%	Diverse, high-quality data
VIVOS	6.83%	Natural conversational data
ViMedCSS	15.68%	Medical field, with English terms
Real business meetings	20.29%	Noisy environment, multiple speakers

Advice for Enterprises Deploying Speech AI

If you are considering deploying speech recognition technology for your business, consider the following points:

1. Don’t just look at low prices: A free open-source model may not be accurate enough for real business needs, especially in critical fields like healthcare, finance, or customer care.
2. Prioritize solutions with localized data: Ask vendors about the origin of their training data. Vietnamese data collected and cleaned in Vietnam always yields better results than translated or synthetic data.
3. Test in real-world environments: Before wide-scale deployment, run trials with actual audio recordings from your own workflow. Measure accuracy in conditions with noise and multiple speakers.

Conclusion

The quality of Vietnamese speech data is the key factor determining the success or failure of AI voice systems. Through the journey of building a 690,517-hour corpus, AIVISION demonstrates that serious investment in data collection, cleaning, and annotation leads to improved accuracy, especially in complex contexts.

For enterprises, choosing a Speech-to-Text platform trained on high-quality data is not just a technology choice, but a strategy to optimize workflows and enhance user experience.

If you want to experience the accuracy of Vietnamese speech recognition technology, Start free today. Explore more AI solutions on our Blog.

Frequently asked questions

Where was AIVISION’s 690,517-hour corpus collected from?

The data was collected from various sources, including everyday conversations, business meetings, and medical and legal content, ensuring diversity in voices, dialects, and usage contexts.

How does AIVISION’s model achieve high accuracy?

The difference mainly comes from AIVISION using a Vietnamese corpus that has been deeply cleaned and annotated, particularly its ability to handle mixed English and real-world environmental noise.

Does AIVISION support English?

Yes, AIVISION’s products support both Vietnamese and English, including natural speech recognition and synthesis for both languages.

How can I start using AIVISION’s API?

You can register an account and get an API key in our console. Currently, every account is provided with a free daily usage allowance to make testing easy.

How much does AIVISION’s service cost?

AIVISION applies a token-based pricing model with flexible payment options. See details at [Pricing](/en/pricing).

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