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What is speech-to-text?

Olga Miroshnyk
Olga Miroshnyk
Dec 29, 2022
3 min read


Speech-to-text, or automatic speech recognition (ASR), technology has been around for a while, but it is only recently that it has gained widespread adoption. ASR allows users to speak commands and control their devices using their voice, making it a popular choice for virtual assistants, captioning and transcription, customer service, education, medical documentation, and legal documentation. According to Forrester's survey, many information workers in North America and Europe use voice commands on their smartphones at least occasionally, with the most common use being texting (56%), searching (46%), and navigation/directions (40%). However, there are still challenges that need to be addressed in order for this technology to reach its full potential. 

In this article, we will explore the different methods of speech-to-text and how it is used in various applications, including transcription services, voice recognition software, and accessibility tools. We'll also take a look at the future of speech-to-text and see how this technology is likely to continue to improve and expand in the coming years. So, let's dive in and see what makes speech-to-text such a powerful tool for businesses and individuals alike.


How speech-to-text technology works 

Speech-to-text technology is a type of natural language processing (NLP) that converts spoken words into written text. It is used in a variety of applications, including voice assistants, transcription services, and accessibility tools. Here is a more detailed explanation of how speech-to-text technology works:

Sound conversion

The first challenge in speech-to-text technology is that sound is analog, while computers can only understand digital inputs. To convert sound into a digital format that computers can understand, a microphone is used. The microphone converts sound waves into an electrical current, which is then converted into voltage and read by a computer.

Frequency isolation

The next step in the process is to isolate individual frequencies from the sound input. This is done using a technique called Fast Fourier Transform (FFT), which converts the sound input into a spectrogram. A spectrogram is a visual representation of sound, with time on the X-axis, frequencies on the Y-axis, and intensity represented by brightness.

Image source: Wikipedia

Phoneme recognition 

It’s the process of identifying the basic building blocks of speech, known as phonemes. This is a crucial step in speech-to-text technology because phonemes are the foundation upon which words are built. There are several different approaches to phoneme recognition, including statistical models like the hidden Markov model and machine learning systems like neural networks.

Neural networks are a type of machine learning system that is made up of interconnected nodes that can adjust their weights based on feedback. A neural network consists of layers of nodes that are organized into an input layer, an output layer, and one or more hidden layers. The input layer receives data, the hidden layers perform transformations on the data, and the output layer produces the final result. Every time the neural network receives feedback, it adjusts the weights of the connections between the nodes to improve its performance.

One advantage of neural networks is that they can adapt to large variations in speech, such as different accents and mispronunciations. However, they do require a large amount of data to be set up and trained, which may be a limitation for some applications. In contrast, statistical models like the hidden Markov model are less data-hungry, but they are unable to adapt to large variations in speech. As a result, it is common to use both types of models in speech-to-text technology, with the hidden Markov model being used to handle basic phoneme recognition and the neural network handling more complex tasks.

Word analysis 

It’s the process of analyzing the sequence of phonemes that make up a word in order to identify the intended meaning. This is done using either a language or an acoustic model.

The language model takes into account the context of the word, as well as the frequency of different phoneme combinations in the language being used. For example, in English, the phoneme "m" is never followed by an "s." Therefore, if the language model encounters the sequence "ms," it will consider it to be an error and attempt to correct it based on the context and the likelihood of different phoneme combinations.

The language model is an important part of speech-to-text technology because it allows the system to understand the meaning of words and sentences. By analyzing the sequence of phonemes and taking into account the context, the language model can determine the intended meaning of spoken words and produce the corresponding written text.

The acoustic model is a statistical model that maps the acoustic features of speech to the corresponding words or phonemes. The acoustic model is trained on a large dataset of audio recordings and the corresponding transcriptions, and it uses this data to learn the patterns and features that are characteristic of the language being used.

During the STT process, the audio input is analyzed by the acoustic model, which produces a sequence of probability scores for each possible word or phoneme. The sequence of scores is then fed into a language model, which takes into account the context and the likelihood of different word combinations to produce the final transcription.

There are several different types of acoustic models, including hidden Markov models (HMMs) and deep neural networks (DNNs). HMMs are statistical model that consists of states and corresponding evidence, and they are commonly used for speech recognition because they are computationally efficient and relatively easy to train. DNNs are a type of machine learning model that consists of layers of interconnected nodes, and they are able to adapt to large variations in speech. DNNs are more data-hungry and require more computational resources to train, but they tend to perform better than HMMs on many speech recognition tasks.

Which model is better or more common for a given language depends on a variety of factors, including the complexity of the language, the amount of data available for training, and the resources available for training and running the model. In general, DNNs tend to perform better on a wide range of tasks, but they may not be the best choice for all languages or situations.

Final transcript

Text output is the final step in converting spoken words or text from one language to another using speech-to-text technology. It involves displaying the translated text on a screen or saving it to a file.

What are STT APIs and their advantages? 

API (Application Programming Interface) is a set of rules and protocols that allows different software systems to communicate with each other. In the context of speech-to-text applications, an API is a set of programming instructions that allows developers to access and use the STT capabilities of a service or platform in their own applications.

There are several different types of voice recognition APIs available, including cloud-based APIs and on-premises APIs. Cloud-based APIs are hosted by a third-party provider and accessed over the internet, while on-premises APIs are installed on a local server and accessed within an organization's network.

Speech-to-text APIs offer plenty of advantages for individuals and businesses:

Increased productivity: Allows users to input text quickly and efficiently using their voice, rather than typing on a keyboard or touchpad. This can save time and increase productivity, especially for tasks that involve a lot of text input.

Improved accessibility: Can be used to provide accessibility features such as live captions and subtitles, which can be helpful for individuals with hearing impairments or learning disabilities.

Enhanced customer experience: Speech-to-text applications can provide various manipulations with recognized and transcribed text, for example, summarization. By getting a quick summary of customer feedback businesses can identify common issues, for example. 

Greater flexibility: STT APIs can be accessed from any device with an internet connection, allowing users to input text using their voice from anywhere.

Cost savings: One of the major benefits for businesses is cost savings. By automating text input tasks, businesses can reduce or eliminate the need for manual transcription services, which can be costly and time-consuming. Additionally, it can help businesses streamline their processes and increase efficiency.

Improved accuracy: Advanced natural language processing algorithms have a high level of accuracy in transcribing spoken words, which can help reduce errors and improve the quality of the resulting text.

Best speech-to-text API applications

There are many speech-to-text (STT) application programming interfaces (APIs) available on the market, and the best one for you will depend on your specific needs and preferences. Here are some popular STT APIs that are widely used and well-regarded by experts:

  • Google Cloud Speech-to-Text API: Use a powerful API to convert speeches into texts accurately with the help of Google Cloud’s Speech-to-Text solution known for its high accuracy and wide range of customization options. It offers an excellent user experience by transcribing your speech with accurate captions.
  • IBM Watson Speech to Text API: IBM Watson Speech to Text offers AI-powered transcription and speech recognition solutions. It enables accurate and fast speech recognition in different languages for various use cases, such as customer self-service, speech analytics, agent assistance, and more.
  • Microsoft Azure Speech Services: Use a powerful API to convert speeches into texts accurately with the help of Google Cloud’s Speech-to-Text solution. It offers an excellent user experience by transcribing your speech with accurate captions. It also helps improve your services through the insights taken and transcribed from your customer interactions.
  • Amazon Transcribe: Amazon Transcribe is a big cloud-based automatic speech recognition platform developed specifically to convert audio to text for apps. It is available for use on a variety of platforms, including Windows, Mac, and mobile devices.
  • OneAI is a language AI service that offers product-ready APIs and pre-trained models for developers. It allows developers to access speech-to-text and audio-intelligence capabilities in a single API call, enabling them to process audio and video into structured data for various purposes such as generating summaries and transcripts, and detecting sentiments and topics.

Use cases of speech-to-text applications

There are many potential use cases for speech-to-text technology. Some of the most common use cases include:

Automated dictation

If you're a content creator, writer, or anyone who needs to type long-form text, STT APIs can be a huge help. You can dictate your words and produce written text, saving time and effort.

Voice control

Speech-to-text can be used to enable voice control of various applications, such as virtual assistants or smart home devices. By issuing voice commands, users can easily interact with these devices and perform a wide range of tasks without having to type or use other input methods.

Medical transcription

In the medical field, this technology can be used to transcribe medical reports, notes, and other documents. This can help to reduce the workload for medical professionals and improve the accuracy of patient records


You can translate spoken words into different languages, which can be particularly useful for people who are traveling or working with people who speak different languages.

Voice biometrics

It’s the process of verifying the identity of a user based on their voice and also can be a task for voice recognition applications. This can be used to enable secure authentication for applications such as banking or online services.


Students with learning disabilities or language barriers can use the benefits of STT applications by getting real-time transcriptions of lectures or other educational materials. This can make learning more accessible and inclusive for all students.

Emotion recognition

Speech-to-text can also be used to analyze certain vocal characteristics to determine what emotion the speaker is feeling. Paired with sentiment analysis, this can reveal how someone feels about a product or service.

Limitations and future of speech-to-text

Like all technology, speech-to-text technology has its limitations. Some of the main limitations include:

Accurate transcription relies on clear speech: voice recognition systems are more likely to produce accurate transcriptions when the spoken words are clear and easily understood. If the speech is distorted or difficult to understand, the accuracy of the transcription may suffer.

Accents and dialects: Voice recognition systems are typically trained on a particular accent or dialect of a language. If the speaker has a different accent or dialect, the accuracy of the transcription may be lower.

Problems with context understanding: STT systems may struggle to understand the context in which words are being used, which can lead to incorrect transcriptions or translations.

Significant computing resources are required: Developing and maintaining voice recognition systems can be resource-intensive, as they require large amounts of data and computing power to train and operate.

Despite these limitations, the future of this technology looks bright. The speech-to-text industry has seen significant growth in recent years, with the global market value expected to reach $28.1 billion by 2027. The increased demand for this technology has led to the development of advanced capabilities such as punctuation, speaker diarization, global language packs, and entity formatting. One major breakthrough in the industry is the introduction of self-supervised learning, which allows STT engines to learn from unstructured data on the internet, giving them access to a wider range of voices and dialects and reducing the need for human supervision.

Universal availability will make ASR accessible to everyone, while the collaboration between humans and machines will allow for the organic learning of new words and speech styles. Finally, responsible AI principles will ensure that ASR operates without bias.


Speech-to-text technology has come a long way in recent years, and its capabilities continue to expand with the development of self-supervised learning and the integration of natural language understanding (NLU). These advancements have enabled speech-to-text systems to learn from a wide range of unstructured data and improve their accuracy in a variety of languages and accents. As a result, STT technology is being utilized in an increasingly diverse range of industries, from healthcare and finance to communications and customer service.

OneAI creates 93% accurate speech-to-text transcriptions and suggests a wide range of Language Skills (use-case ready, vertically pre-trained models) like summarization, proofreading, sentiment analysis, and many more. Just check our Language Studio and pick those which will increase the efficiency of your business. 

Command Your World with Speech-to-Text!


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