Speech-To-Text Conversion – How Does It Work?

Speech-To-Text TechnologySpeech-to-text conversion is the process of converting spoken words into written text. Often referred to as speech recognition, the process of speech-to-text conversion uses systems that rely on at least two models: an acoustic model and a language model.

Additionally, vocabulary systems use a pronunciation model. These systems are widely used in the audio transcription industry where they are specialized for a given language, dialect, type of speech, application domain, or communication channel to ensure best quality transcription.

Regardless of the model being used or the specialized features, the conversion process is usually done in the following three steps.

Converting Audio   

The first step of the complex process of converting speech to on-screen text begins by translating audio into a language that the computer can understand. By speaking, we create vibrations in the air. These vibrations are picked up by an analog-to-digital convertor, which then translates them into digital data that is recognizable by a computer. The convertor samples or digitizes sound by taking precise measurements of the vibration at frequent intervals.

Generally, the higher the sampling and precision rates, the higher the quality of the transcription end-product. The speech-to-text system then filters the digitized sound by removing unwanted noise and sometimes separating it into different bands of frequency. The system also normalizes the sound or adjusts it to a constant volume level to ensure accuracy during transcription.

Breaking Speech Into Segments

The second step entails the breakdown of the digital data into small segments as short as a few hundredths or thousandths of a second. The segments are then matched to known phonemes in the appropriate language of the particular voice-recognition software being used.

Phonemes are the smallest elements of a language that distinguish one word from another. For example, ‘p’ and ‘b’ in the English words ‘Pad’ and ‘Bad’. This step facilitates the final act of converting audio into text by helping the computer recognize every single syllable of the language being spoken. A speaker with a heavy accent can affect this step resulting in poor quality transcription.

Conversion Of Speech Segments

The final step is the focus of most speech recognition research as it is the most difficult to achieve. The quality of the text document produced depends on the effectiveness of a computer to carry out this step. It includes the examination of phonemes in the context of other phonemes around them. The computer program then runs the contextual phoneme plot through a complex statistical model and compares them to a large library of known words, sentences, and phrases. The program then determines what the user was saying and either puts it into text or issues a computer command.

So there you have it, the different steps involved in converting audio files into text. A range of speech-to-text software programs allow transcriptionists dictate to computers and have the speech converted into text in a word processing or e-mail document. With these software programs, command functions such as opening files, accessing menus, and inputting content, is done through voice instructions. Some programs are specific to certain business settings such as legal and medical transcription.

Euan Macintyre is an audio and video recording professional who loves writing about the latest software programs related to his area of expertise. He also writes for audio transcription service providers. Click here to visit Euan’s favorite transcription service.