A Quick Look at Audio Classification & Signal Retrieval

Published on Wednesday October 12, 2022 5 min read By Anolytics
A Quick Look at Audio Classification & Signal Retrieval

Audio data is becoming increasingly prevalent on public networks, particularly on Internet-based platforms. It is, therefore, essential for us to index and annotate this audio data efficiently in order to have uninterrupted access to it. The nonstationary nature of audio signals and their discontinuities make segmenting and classifying them highly challenging tasks. The difficulty in extracting and selecting optimal audio features also makes automatic music classification and annotation difficult.

Music retrieval, speech recognition, and acoustic surveillance are among the applications of content-based audio retrieval systems today. Identifying content-based characteristics for the representation of audio signals is a major challenge during the development of audio retrieval systems. There are various techniques for analyzing and retrieving audio signals. This paper provides a fleeting glimpse into these techniques alongside introducing a novel approach to audio signal analysis and retrieval.

What is Audio Annotation?

It is important to note that audio annotation is a subset of data annotation, which is important in building effective natural language processing (NLP) models. Today, audio annotation offers many benefits to organizations, such as analyzing text, speeding up customer responses, and recognizing human emotions. The audio annotation process involves categorizing audio elements that originate from everything around us, e.g., humans, animals, instruments, and other sound-producing elements in the environment.

Among the data formats, engineers use for annotation are MP3, FLAC, AAC, and others. The process of annotating audio (as with annotating images and text) requires manual labor and software precisely optimized for the purpose. To train the NLP model, data scientists specify the audio-specific information and pass it along to software that specifies the labels or “tags.”

Significance of Audio Annotation

Voice recognition security systems, virtual assistants, chatbots, and other technologies rely heavily on audio annotation. In enterprises, NLP ranks third among AI-related technologies. A survey from 2017 found that 53% of companies employed some form of NLP in their business processes.

It is estimated that revenue for the NLP market will reach over $43 billion by 2025 at a yearly growth rate of about 25%. Thus, audio labeling is a crucial task in the modern world.

Digitalized and fast customer service is also increasingly demanded by customers. Therefore, chatbots are becoming increasingly important to customer service, and the quality of audio annotation directly affects the quality of chatbots.

Audio Annotation

An audio annotation can be accomplished in five ways:

Speech-to-Text Transcription: For developing NLP models, it is essential to accurately transcribe speech into text. Recording speech and converting it into text, marking words and sounds as they are pronounced, is required for this technique. The correct use of punctuation is also crucial in this technique.

Audio Classification: Machines can distinguish between voices and sounds by using this technique. It is imperative to use this type of audio labeling when developing virtual assistants, as it allows the AI model to recognize who is speaking.

Natural Language Utterance: Human speech is annotated using natural language to distinguish semantics, dialects, contexts, intonations, etc. It is, therefore, important to train chatbots and virtual assistants using natural language utterances.

Speech Labeling: A data annotator labels sound recordings with keywords after extracting the required sounds. Chatbots using this method can handle repetitive tasks.

Music Classification: Data annotators can use audio annotation to mark genres or instruments. Music classification is significant for keeping music libraries organized and refining user recommendations.

Audio annotation is highly dependent on high-quality audio data. Through a platform-agnostic annotation approach and in-house workforce, Anolytics can meet your audio data needs. We can help you get the audio training data you need for your purpose.

Sound Classification

Sound Classification, which involves classifying or categorizing different sounds, is one of the most widely used applications in Audio Deep Learning. Noise monitoring, animal call classification, and music information retrieval are among the many applications of sound classification in machine listening. Supervised learning is typically used to train modern sound classification models. A robust model must be trained on large amounts of labeled data for supervised learning.

Human annotation is one method for obtaining labeled audio data, but it can be labor-intensive. Many problems exhibit unusual sound classes unique to the problem, e.g., unusual failure rates of machines and sensors. This cost can be justified if the data can be reused for several problems. Consequently, existing data for such tasks would be of little use, and we would have to collect new data that would be of minimal use for other tasks — resulting in an increased cost per task for annotation.

Audio Retrieval

Today’s audio retrieval techniques successfully apply to text documents, testified to by the huge commercial profits generated by search engine companies like Google and Yahoo. For multimedia data retrieval, no existing product or tool has offered user satisfaction or popularity compared to text-based search engines.

Various fields of research exist in content-based audio retrievals, such as segmentation, automatic speech recognition, music information retrieval, and environmental sound retrieval. Segmentation distinguishes different types of sound such as speech, music, silence, and environmental sounds. It is an essential preprocessing step that identifies homogenous parts in an audio stream. It also helps to further analyze the different audio types using appropriate techniques.

  1. Automatic speech recognition recognizes the spoken word on the syntactic level.
  2. Music information retrieval has become a popular domain in the last decade. It deals with retrieving similar pieces of music, instruments, artists, and genres and analyzing musical structures. It also focuses on music transcription, which aims at extracting the pitch, pace, duration, and signal source of each sound in an audio file.
  3. Environmental sound retrieval comprises all types of sound that are neither speech nor music.

The main objective of content-based audio retrieval is to identify perceptually similar audio content. But this task is often trivial for humans because of powerful mechanisms in our brains. The human brain can easily distinguish between wide ranges of sound and correctly assign them to semantic categories and previously heard sounds. This, in turn, is much more difficult for computer systems, where an audio signal is simply represented by a numeric series of samples without any semantic meaning.

The typical architecture of a content-based audio retrieval system consists of three modules, namely the input module, the query module, and the retrieval module. The input module extracts features from audio objects stored in an audio database. In feature extraction, meaningful information is extracted from the signal to reduce the amount of data.

Automated vs. Human-empowered Audio Annotation

Companies need software that specializes in the audio annotation. You can access third-party audio annotation tools that offer open-source and closed-source software. Audio annotation tools that are open source are free and can be customized to meet your organization’s needs because the code is available to everyone. Unlike open-source automated audio annotation tools, closed-source tools are supported by a team of experts. However, it may incur some cost.

Developing your audio annotation software could be an alternative to outsourcing. The process is, however, costly and slow. Getting audio annotation done by an outsourced team of experts can bring a bucket of benefits regarding data security. It is, therefore, wise to pick an outsourced audio annotation and classification expert to accomplish the audio annotation assignments.

Outsourced Audio Annotation

What sets you out in picking the right audio annotation partner to get you sorted for the sound classification or annotation requirements? While sticking to your very own in-house team of audio annotation experts can be a costly affair, relying on crowdsourced experts might pose a severe threat to your data security. The best is to have an industry expert with an established name in the market for quality audio annotation services, as Anolytics has. The right choice to collaborate with for your audio annotation requirements is the one that can promise privacy and security to your data.

It is undeniably true that the optimal approach that one chooses for audio annotation entirely depends on the actual annotation requirements of the organization, its workforce, and financial capabilities. However, investing in an outsourced audio annotation partner can be a cost-saving deal, bringing you tons of data security benefits, high-quality annotation, and timely accomplishments.

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