Working with WAV files for the DSP study group

Author: onbreath

src/dsp/18871__zippi1__sound-bell-440hz-compressed.wav

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+^{:kindly/hide-code true
+  :clay {:title "DSP Study Group - Reading audio data from WAV-files"
+         :quarto {:author [:daslu :onbreath]
+                  :description "Exploring WAV-files for DSP in Clojure."
+                  :category :clojure
+                  :type :post
+                  :date "2025-11-09"
+                  :tags [:dsp :math :music]
+                  :image "wav.png"
+                  :draft true}}}
+(ns dsp.wav-files
+  (:require [scicloj.kindly.v4.kind :as kind]
+            [clojure.java.io :as io]
+            [tech.v3.datatype.functional :as dfn]
+            [tablecloth.api :as tc]
+            [scicloj.tableplot.v1.plotly :as plotly])
+  (:import (javax.sound.sampled AudioFileFormat
+                                AudioInputStream
+                                AudioSystem)
+           (java.io InputStream)
+           (java.nio ByteBuffer
+                     ByteOrder)))
+
+;; **Exploration from the [Scicloj DSP Study Group](https://scicloj.github.io/docs/community/groups/dsp-study/)**
+;; *Second meeting - Nov. 08th 2025 and some follow-up investigation*
+
+;; Welcome! These are notes from our second study group session, where
+;; we're learning digital signal processing together using
+;; Clojure. We're following the excellent book
+;; [**Think DSP** by Allen B. Downey](https://greenteapress.com/wp/think-dsp/) (available free online).
+;;
+;; **Huge thanks to Professor Downey** for writing such an accessible and free introduction to DSP, and for sharing with us the work-in-progress notebooks of [Think DSP 2](https://allendowney.github.io/ThinkDSP2/index.html).
+
+;; Along with this study group came the idea to have an online
+;; creative coding festival around Clojure in the first months of
+;; 2026. In this meeting we spent some time brainstorming on how that
+;; might look and what the scope could be. The remaining time of the
+;; session we looked into downloading and reading WAV-files in
+;; Clojure.
+
+;; ## Why WAV Files?
+;;
+;; The notebooks in Think DSP 2 work with WAV files loaded from GitHub
+;; as a basis for further processing, so we need a way to load these
+;; as well. After obtaining the file, we need to get at the audio data
+;; it contains.
+
+;; ## Simplified WAV Format
+
+;; First, let's take a superficial look at what data WAV files
+;; contain, before we dive into getting the data. A simple WAV file
+;; consists of a header and pure audio data following it. There are
+;; several iterations on specifications for the WAV format and the
+;; format allows for quite some flexibility in placing different
+;; metadata in the file, as well as different encodings.
+
+^:kindly/hide-code
+(kind/mermaid
+ "---
+config:
+    theme: 'forest'
+---
+
+block
+    columns 1
+    block:wav
+        columns 5
+        block:HeaderId
+            columns 1
+            HeaderLabel[\"Header\"]
+        end
+
+        block:F1
+            columns 1
+            FrameLabel1[\"Frame\"]
+        end
+
+        block:F2
+            columns 1
+            FrameLabel2[\"Frame\"]
+        end
+
+        block:F3
+            columns 1
+            FrameLabel3[\"Frame\"]
+        end
+
+        block:FN
+            columns 1
+            FrameLabelN[\"...\"]
+        end
+    end")
+
+
+;; The WAV (Waveform Audio File Format) file format is a
+;; RIFF (Resource Interchange File Format) file which stores data in
+;; **chunks**. Each **chunk** consists of a **tag** and **data**. Lets
+;; consider a partial example, which corresponds to the way the WAV
+;; file we want to read is arranged:
+
+^:kindly/hide-code
+(kind/mermaid
+ "---
+config:
+    theme: 'forest'
+---
+
+block
+    columns 1
+    block:wav
+        columns 3
+        block:HeaderId
+            columns 1
+            HeaderLine1[\"RIFF\"]
+            HeaderLine2[\"WAVE\"]
+        end
+
+        block:HeaderId2
+            columns 1
+            HeaderLine3[\"fmt \"]
+            HeaderLine4[\"1\"]
+            HeaderLine5[\"44100\"]
+            HeaderLine6[\"16\"]
+        end
+
+        block:data
+            columns 1
+            DataLabel[\"data\"]
+            ChanF1[\"ch0\"]
+            ChanF2[\"ch0\"]
+            ChanF2[\"ch0\"]
+            ChanF3[\"ch0\"]
+            ChanFN[\"...\"]
+        end
+    end")
+
+;; The header comprises of the **tag** `RIFF`, its **chunk** tagged
+;; with the specific format `WAVE` and a **subchunk** `fmt `, which
+;; describes the contained audio data.  This represents some of the
+;; header information in a WAV file with a single, 16-bit mono sound
+;; channel and 44.100 samples per second.
+
+;; As we learned in the [first session](https://clojurecivitas.github.io/dsp/intro.html)
+;; of the DSP study group:
+;; > Sound waves are continuous vibrations in the air. To work with them on a computer,
+;; > we need to **sample** them - take measurements at regular intervals. The **sample rate**
+;; > tells us how many measurements per second. CD-quality audio uses 44,100 samples per second.
+
+;; These **samples** are stored in the WAV files `data` tagged
+;; **subchunk**. Since this is mono sound, there is one **frame** with
+;; one **channel** per **sample**. For multiple **channels**, each
+;; **frame** consists of all channels and their respective **sample**.
+
+;; ## Libraries We're Using
+;;
+;; - **[Kindly](https://scicloj.github.io/kindly-noted/kindly)** - Visualization protocol that renders our data as interactive HTML elements (through Clay)
+;; - **[Kindly](https://scicloj.github.io/kindly-noted/kindly)** - Visualization protocol that renders our data as interactive HTML elements (through Clay)
+;; - **[dtype-next](https://github.com/cnuernber/dtype-next)** - Efficient numerical arrays and vectorized operations (like NumPy for Clojure)
+;; - **[Tablecloth](https://scicloj.github.io/tablecloth/)** - DataFrame library for data manipulation and transformation
+;; - **[Tableplot](https://scicloj.github.io/tableplot/)** - Declarative plotting library built on Plotly
+;; - **[javax.sound.sampled](https://docs.oracle.com/en/java/javase/25/docs/api/java.desktop/javax/sound/sampled/package-summary.html)** - Some classes from the Java standard libraries sound package to read WAV Files.
+
+(require '[scicloj.kindly.v4.kind :as kind]
+         '[clojure.java.io :as io])
+^:kindly/hide-code
+(kind/code
+ "(import '(javax.sound.sampled AudioFileFormat
+                              AudioInputStream
+                              AudioSystem)
+        '(java.io InputStream)
+        '(java.nio ByteBuffer
+                   ByteOrder))")
+
+
+;; ## Downloading a WAV File
+(defn copy [uri file]
+  (with-open [in (io/input-stream uri)
+              out (io/output-stream file)]
+    (io/copy in out)))
+
+^:kindly/hide-code
+(def tuning-fork-file
+  "18871__zippi1__sound-bell-440hz.wav")
+
+^:kindly/hide-code
+(def tuning-fork-url
+  (str "https://github.com/AllenDowney/ThinkDSP/raw/master/code/" tuning-fork-file))
+
+^:kindly/hide-code
+(def tuning-fork-file
+  "18871__zippi1__sound-bell-440hz.wav")
+
+^:kindly/hide-code
+(def tuning-fork-file-compressed
+  "18871__zippi1__sound-bell-440hz-compressed.wav")
+
+^:kindly/hide-code
+(def tuning-fork-path
+  (str "src/dsp/" tuning-fork-file))
+
+^:kindly/hide-code
+(def tuning-fork-path-compressed
+  (str "src/dsp/" tuning-fork-file-compressed))
+
+(copy tuning-fork-url tuning-fork-path)
+
+;; ## Playing a WAV File
+;;
+;; Kindly can embed a player with a URL, but the sample is extremely
+;; loud (it is a tuning fork struck in front of a microphone), so we
+;; don't embed this player.
+^:kindly/hide-code
+(kind/code "(kind/audio {:src tuning-fork-url})")
+
+;; Here we use a compressed and loudness normalized version of the
+;; original file, so you can safely listen to it.
+(kind/audio {:src tuning-fork-file-compressed})
+
+;; ## Reading Metadata from the WAV File
+;;
+;; We define a function to collect some metadata from the file.
+(defn audio-format [^InputStream is]
+  (let [file-format (AudioSystem/getAudioFileFormat is)
+        format      (.getFormat file-format)]
+    {:is-big-endian?   (.isBigEndian format)
+     :channels         (.getChannels format)
+     :sample-rate      (.getSampleRate format)
+     :sample-size-bits (.getSampleSizeInBits format)
+     :frame-length     (.getFrameLength file-format)
+     :encoding         (str (.getEncoding format))}))
+
+(with-open [wav-stream (io/input-stream tuning-fork-path)]
+  (def wav-format
+    (audio-format wav-stream)))
+
+wav-format
+
+;; `:is-big-endian?` specifies the byte order of audio data with more
+;; than 8 `:sample-size-bits`. `:sample-size-bits` is the number of
+;; bits comprising a sample. The `:frame-length` is the total amount
+;; of frames contained in the audio data.
+
+;; We don't use much of that information for now, but it'll let us
+;; peek at what kind of WAV file we're working with in the future and
+;; we can use the information to extend our function for extracting
+;; audio data, which we define next.
+
+;; ## Reading Audio Data from the WAV File
+;;
+;; The bulk of work here is handled by the ``AudionInputStream``, but
+;; since it only reads bytes for us, we have to put these together
+;; into the correct datatype for each frame manually. For now we just
+;; put the data for 16-bit mono WAV files into a short-array.
+(defn audio-data [^InputStream is]
+  (let [{:keys [frame-length]} (audio-format is)
+        format                 (-> (AudioSystem/getAudioFileFormat is)
+                                   AudioFileFormat/.getFormat)
+        ^bytes audio-bytes     (with-open [ais (AudioInputStream. is format frame-length)]
+                                 (AudioInputStream/.readAllBytes ais))
+        audio-shorts           (short-array frame-length)
+        bb                     (ByteBuffer/allocate 2)]
+    (dotimes [i frame-length]
+      (ByteBuffer/.clear bb)
+      (.order bb ByteOrder/LITTLE_ENDIAN)
+      (.put bb ^byte (aget audio-bytes (* 2 i)))
+      (.put bb ^byte (aget audio-bytes (inc (* 2 i))))
+      (aset-short audio-shorts i (.getShort bb 0)))
+    audio-shorts))
+
+(with-open [wav-stream (io/input-stream tuning-fork-path)]
+  (def wav-shorts
+    (audio-data wav-stream)))
+
+;; The difference between the WAV file bytes and the audio data we
+;; read is 44 bytes, which is the size of the default header and
+;; container.
+(with-open [wav-stream (io/input-stream tuning-fork-path)]
+  (- (count (.readAllBytes wav-stream))
+     (* 2 (count wav-shorts))))
+
+;; ## Striking the Fork
+;;
+;; Now that we have read the data we can reduce its amplitude, so we
+;; can listen to it safely.
+^kind/audio
+{:samples (dfn// wav-shorts 4000000.0)
+ :sample-rate (:sample-rate wav-format)}
+
+;; In fact, the function `audio-data` above is quite similar to how [Clay](https://github.com/scicloj/clay/blob/main/src/scicloj/clay/v2/item.clj#L420) writes the audio data to a file for us to listen to in the browser, just the reverse of what we did for reading.
+
+;; ## Visualizing Waves
+;;
+;; Let's take a look at the sound of a tuning fork.
+(let [{:keys [frame-length sample-rate]} wav-format]
+  (-> {:time (dfn// (range frame-length)
+                    sample-rate)
+       :value wav-shorts}
+      tc/dataset
+      (plotly/layer-line {:=x :time
+                          :=y :value})))
+
+;; ## What we learned
+;;
+;; In the second session and some pairing beyond we prepared for our
+;; forthcoming sessions on Think DSP by:
+;; - **WAV file format** - Learning about the structure of simple WAV files
+;; - **File download** - Downloading files with Java
+;; - **WAV file metadata** - Reading metadata of a WAV file
+;; - **WAV file audio data** - Reading the bytes in the audio data container and converting them to an appropriate data type
+;;
+;; ## Next Steps
+;;
+;; In our next study group meetings, we'll explore the book step by step, and learn more about sounds and signals,
+;; harmonics and the Forier transform, non-periodic signals and spectograms, noise and filtering, and more.
+;;
+;; Join us at the [Scicloj DSP Study Group](https://scicloj.github.io/docs/community/groups/dsp-study/)!
+;;
+;; ---
+;;
+;; *Again, huge thanks to Allen B. Downey for Think DSP. If you find this resource valuable,
+;; consider [supporting his work](https://greenteapress.com/wp/) or sharing it with others.*