Autosave: 2025-01-01 15:57:56

neuron/3cd71ed3-2c64-460c-92b8-94889befa1fe/Binary_encoding_of_sound.md

@@ -1,9 +0,0 @@
----
-tags: []
-created: Friday, December 27, 2024 
----
-# Binary_encoding_of_sound
-
-
-
-

neuron/3cd71ed3-2c64-460c-92b8-94889befa1fe/SQLite.md

@@ -1,25 +0,0 @@
----
-tags: [databases, SQL, SQLite]
-created: Wednesday, November 13, 2024
----
-
-# SQLite
-
-## Enabling foreign key constraints
-
-Foreign key constraints are not enabled by default - it is very permissive. You
-must manually turn them on, as part of the connection process:
-
-```py
-connection = sqlite3.connect("my_database.db")
-connection.execute("PRAGMA foreign_keys = ON")
-```
-
-## INSERT OR IGNORE INTO
-
-If table has a `UNIQUE` constraint on a field, insert if it is unique otherwise
-skip without throwing a constraint error.
-
-```sql
-INSERT OR IGNORE INTO table_name (value) VALUES (:value)
-```

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/Audio_file_formats.md

@@ -5,44 +5,57 @@ created: Friday, December 27, 2024
 
 # Audio file formats
 
-## CD
+## CD quality
 
-- CDs store audio in uncompressed PCM (Pulse Code Modulation) format
-- They have a sampling rate of 44.1kHz
-- In two channels for stereo
+We can use CD's as the digital gold standard as the best digital quality
+available (to consumers).
 
-## WAV: Waveform Audio File Format
+CDs store audio in uncompressed PCM (Pulse Code Modulation) format.
+
+They have a sampling rate of 44.1kHz, which is done in two channels to enable
+stereo.
+
+## What lossy formats entail
+
+A conversion to MP3 from, for example, a CD source is always a one-way process
+and is not reversible. Once information is discarded in the compression process,
+it cannot be retrieved.
+
+This is obviously in contrast to lossless methods like FLAC where the original
+CD audio can always be reconstructed.
+
+It follows from the above that if you repeatedly encode a CD source to MP3, it
+will deteriorate in quality since more data is being removed each time.
+
+## Major audio formats
+
+### WAV (Waveform Audio File Format)
 
 - CD-quality encoding with no compression
 - Bit-for-bit identical to the CD source
 - Historically developed for Windows machines but can play on all operating
   systems
 
-## FLAC: Free Lossless Audio Codec
+### FLAC (Free Lossless Audio Codec)
 
 - Basically the same as WAV but in a (losslessly) compressed format
 - The difference between a novel in a text file (WAV) and as a zipped file
 
-## MP3: MPEG-1 Audio Layer MP3
+### MP3 (MPEG-1 Audio Layer MP3)
 
 - Lossy format.
 - When a WAV file (or other lossless format) is converted to MP3 a Fast Fourier
-  Transform analysis is performed to determine the frequency of certain sounds.
+  Transform analysis is performed to determine the frequency of certain sounds
 - This is used by the encoder to decide which parts of the sound are
   imperceptible and thus which can be discarded to reduce the file size. This is
   done through the application of psycho-acoustic models.
 - The remaining data is then compressed
 - Examples of the data reduction applied:
+
   - Removing frequencies that humans cannot hear
   - Removing quieter sounds that are masked by louder sounds
   - Combining similar frequencies
   - Reducing stero information where it is less noticable
-- A conversion to MP3 from, for example, a CD source is always a one-way process
-  and is not reversible. Once information is discarded in the compression
-  process it cannot be retrieved. This is obviously in contrast to lossless
-  methods like FLAC where the original CD audio can always be reconstructed.
-- It follows from the above that if you repeatedly encode a CD source to MP3, it
-  will deteriorate in quality since more data is being removed each time.
 
 ## OGG: Ogg Vorbis
 

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/Binary_encoding_of_sound.md

@@ -0,0 +1,50 @@
+---
+tags: [sound, binary, analogue]
+created: Friday, December 27, 2024
+---
+
+# Binary encoding of sound
+
+Sound is a change in air pressure.
+
+To record sound, we convert the change in air pressure into an electrical signal
+by means of a microphone. Effectively, the same natural waveform is converted
+from one medium (the vibration of air molecules) into another medium (electrical
+charge in a field) whilst retaining the same morphology. See
+[Recording and processing sound]().
+
+The resulting electrical signal is analogue: it has a continuous and variable
+frequency and amplitude and thus can have any value at any given moment.
+
+To encode this information digitally we need to make the continuous analogue
+single discrete, so that it can represented with a finite set of symbols (bits).
+
+This process is known as **quantization** and consists in sampling the analogue
+waveform. This means taking a measurement of it at different points in time -
+each second.
+
+CDs sample the audio source at a rate of 44.1 kHz: 44, 100 measurements of the
+signal per second.
+
+The measurements are then stored in a digital format: bits. The amount of bits
+used to record the measurement is the **bit-depth**. Each measurement is rounded
+to the nearest available digital value. CDs have a depth of 16 bits. Thus each
+measurement can be one of $16^2 = 65,536$ possible values.
+
+With sampling at a given bit-depth established, the **bitrate** can be derived.
+
+This is the sampling rate (number of measurements per second) divided by the
+number of bits per sample (bit-depth), multiplied by the number of channels.
+
+Thus for stereo CDs this is:
+
+$$
+(44100 / 16 ) \middot 2 = 1411200
+$$
+
+Or 1.4 Mb/s
+
+> Even with a high bitrate (as with CDs) the process still necessarily involves
+> a loss of information when converting sound from analogue to digital. However,
+> given a high enough value for the sampling rate and bit-depth, the differences
+> are imperceptible to the human ear.

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/SQLite.md

@@ -0,0 +1,59 @@
+---
+tags: [databases, SQL, SQLite]
+created: Wednesday, November 13, 2024
+---
+
+# SQLite
+
+## Enabling foreign key constraints
+
+Foreign key constraints are not enabled by default - it is very permissive. You
+must manually turn them on, as part of the connection process:
+
+```py
+connection = sqlite3.connect("my_database.db")
+connection.execute("PRAGMA foreign_keys = ON")
+```
+
+## INSERT OR IGNORE INTO
+
+If table has a `UNIQUE` constraint on a field, insert if it is unique otherwise
+skip without throwing a constraint error.
+
+```sql
+INSERT OR IGNORE INTO table_name (value) VALUES (:value)
+```
+
+## exec and fetchall
+
+For `CREATE`, `INSERT`, `UPDATE`, `DELETE` operations it is sufficient to simply
+use `execute` to carry out the operations:
+
+```py
+cursor = connection.cursor()
+cursor.execute(sql)
+```
+
+For `SELECT` operations, you must add a return statement that uses `fetchall`:
+
+```py
+sql = "SELECT * FROM table"
+cursor = connection.cursor()
+cursor.execute(sql)
+return cursor.fetchall()
+```
+
+## SELECT response data type
+
+A `SELECT` operation returns a [list](Lists_in_Python.md) of
+[tuples](Tuples_in_Python.md) where each entry in the tuple is a returned field.
+
+For example:
+
+```py
+entries_sql = "SELECT title, size FROM entries"
+
+entries_response = cursor.execute(entries_sql)
+print(cursor.fetchall())
+# [('Lorem ipsum', 127), ('Dolar sit', 4231)]
+```

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/Type_hinting.md

@@ -63,6 +63,35 @@ We could then use it thus:
 def parse_articles() -> list[ArticleInfo]:
 ```
 
+### Explicit type construction
+
+Sometimes, simply asserting that custom type will be returned by a function is
+not sufficient to pass the type checks. In these cases you need to explicitly
+construct the type within the function.
+
+For example this generates an error as Python sees the `tags` type as
+`[Dictionary]`, even though it matches the type:
+
+```python
+class IGraphNode(TypedDict):
+    id: str
+    type: str
+
+```
+
+```py
+tags = [{"id": f"#{tag[0]}", "type": "tag"} for tag in tags]
+```
+
+So you have to explicitly generate the type like this:
+
+```python
+tags = [IGraphNode(id=f"#{tag[0]}", type="tag") for tag in tags]
+```
+
+Then you will be able to type the return of the function as
+`-> list[IGraphNode]`
+
 ## Optional types
 
 `Optional` can be used to indicate that a variable can be `None` or the

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/Working_with_JSON_in_Python.md

@@ -1,5 +1,4 @@
 ---
-id: mjia
 tags: [python, JSON]
 created: Tuesday, June 25, 2024
 ---
@@ -20,8 +19,13 @@ Will error if the input string is not properly formatted JSON. This will be
 Take a JSON-formatted dictionary and convert it into a string. The reverse of
 `json.loads()` and equivalent to `JSON.stringify()` in JavaScript.
 
-## JSON errors
+## `json.dump()`
 
-The `.loads()` and `.parse()` methods will throw an error if the input string is
+Not to be confused with the above. Output a Python dictionary as JSON, for
+instance to create a `.json` file:
 
-## Related notes
+```py
+data = { "key": "value"}
+with open("some/directory/output.json", "w") as f:
+    json.dump(data, f, indent=4)
+```

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/dfsdfdf/Welcome.md

@@ -0,0 +1,5 @@
+This is your new *vault*.
+
+Make a note of something, [[create a link]], or try [the Importer](https://help.obsidian.md/Plugins/Importer)!
+
+When you're ready, delete this note and make the vault your own.

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/eolas testg/Welcome.md

@@ -0,0 +1,5 @@
+This is your new *vault*.
+
+Make a note of something, [[create a link]], or try [the Importer](https://help.obsidian.md/Plugins/Importer)!
+
+When you're ready, delete this note and make the vault your own.

neuron/8f51653f-9574-4f79-81a8-1f2ecc0ba592/index.md

@@ -13,14 +13,17 @@ computer science.
 
 ![not-by-ai-badge](static/not-by-ai-alternative--light.svg)
  
-**Build ID:** 3cd71ed3-2c64-460c-92b8-94889befa1fe
+**Build ID:** 8f51653f-9574-4f79-81a8-1f2ecc0ba592
 
-**Published:** Fri 27 Dec 2024 14:21:54
+**Published:** Wed 01 Jan 2025 15:57:54
 
 ### Recent edits 
 
-- [[Audio_file_formats]] 
 - [[Binary_encoding_of_sound]] 
+- [[Audio_file_formats]] 
+- [[Type_hinting]] 
+- [[Working_with_JSON_in_Python]] 
+- [[SQLite]] 
 - [[a4601796_trapdoor_functions]] 
 - [[bbdcb54f_public_key_cryptography]] 
 - [[Dynamic_and_static_websites]] 
@@ -28,9 +31,6 @@ computer science.
 - [[Architecture_of_the_World_Wide_Web]] 
 - [[Network_packet_analysis_tools]] 
 - [[What_can_the_ISP_see]] 
-- [[HTTPS]] 
-- [[Bauman_quote]] 
-- [[fbbfbc32-political-accommodation-inveigelment-surveillance-capitalism]] 
 
 
 ### All notes (511) 

zk/Audio_file_formats.md

@@ -5,44 +5,57 @@ created: Friday, December 27, 2024
 
 # Audio file formats
 
-## CD
+## CD quality
 
-- CDs store audio in uncompressed PCM (Pulse Code Modulation) format
-- They have a sampling rate of 44.1kHz
-- In two channels for stereo
+We can use CD's as the digital gold standard as the best digital quality
+available (to consumers).
 
-## WAV: Waveform Audio File Format
+CDs store audio in uncompressed PCM (Pulse Code Modulation) format.
+
+They have a sampling rate of 44.1kHz, which is done in two channels to enable
+stereo.
+
+## What lossy formats entail
+
+A conversion to MP3 from, for example, a CD source is always a one-way process
+and is not reversible. Once information is discarded in the compression process,
+it cannot be retrieved.
+
+This is obviously in contrast to lossless methods like FLAC where the original
+CD audio can always be reconstructed.
+
+It follows from the above that if you repeatedly encode a CD source to MP3, it
+will deteriorate in quality since more data is being removed each time.
+
+## Major audio formats
+
+### WAV (Waveform Audio File Format)
 
 - CD-quality encoding with no compression
 - Bit-for-bit identical to the CD source
 - Historically developed for Windows machines but can play on all operating
   systems
 
-## FLAC: Free Lossless Audio Codec
+### FLAC (Free Lossless Audio Codec)
 
 - Basically the same as WAV but in a (losslessly) compressed format
 - The difference between a novel in a text file (WAV) and as a zipped file
 
-## MP3: MPEG-1 Audio Layer MP3
+### MP3 (MPEG-1 Audio Layer MP3)
 
 - Lossy format.
 - When a WAV file (or other lossless format) is converted to MP3 a Fast Fourier
-  Transform analysis is performed to determine the frequency of certain sounds.
+  Transform analysis is performed to determine the frequency of certain sounds
 - This is used by the encoder to decide which parts of the sound are
   imperceptible and thus which can be discarded to reduce the file size. This is
   done through the application of psycho-acoustic models.
 - The remaining data is then compressed
 - Examples of the data reduction applied:
+
   - Removing frequencies that humans cannot hear
   - Removing quieter sounds that are masked by louder sounds
   - Combining similar frequencies
   - Reducing stero information where it is less noticable
-- A conversion to MP3 from, for example, a CD source is always a one-way process
-  and is not reversible. Once information is discarded in the compression
-  process it cannot be retrieved. This is obviously in contrast to lossless
-  methods like FLAC where the original CD audio can always be reconstructed.
-- It follows from the above that if you repeatedly encode a CD source to MP3, it
-  will deteriorate in quality since more data is being removed each time.
 
 ## OGG: Ogg Vorbis
 

zk/Binary_encoding_of_sound.md

@@ -1,9 +1,50 @@
 ---
-tags: []
-created: Friday, December 27, 2024 
+tags: [sound, binary, analogue]
+created: Friday, December 27, 2024
 ---
-# Binary_encoding_of_sound
 
+# Binary encoding of sound
 
+Sound is a change in air pressure.
 
+To record sound, we convert the change in air pressure into an electrical signal
+by means of a microphone. Effectively, the same natural waveform is converted
+from one medium (the vibration of air molecules) into another medium (electrical
+charge in a field) whilst retaining the same morphology. See
+[Recording and processing sound]().
 
+The resulting electrical signal is analogue: it has a continuous and variable
+frequency and amplitude and thus can have any value at any given moment.
+
+To encode this information digitally we need to make the continuous analogue
+single discrete, so that it can represented with a finite set of symbols (bits).
+
+This process is known as **quantization** and consists in sampling the analogue
+waveform. This means taking a measurement of it at different points in time -
+each second.
+
+CDs sample the audio source at a rate of 44.1 kHz: 44, 100 measurements of the
+signal per second.
+
+The measurements are then stored in a digital format: bits. The amount of bits
+used to record the measurement is the **bit-depth**. Each measurement is rounded
+to the nearest available digital value. CDs have a depth of 16 bits. Thus each
+measurement can be one of $16^2 = 65,536$ possible values.
+
+With sampling at a given bit-depth established, the **bitrate** can be derived.
+
+This is the sampling rate (number of measurements per second) divided by the
+number of bits per sample (bit-depth), multiplied by the number of channels.
+
+Thus for stereo CDs this is:
+
+$$
+(44100 / 16 ) \middot 2 = 1411200
+$$
+
+Or 1.4 Mb/s
+
+> Even with a high bitrate (as with CDs) the process still necessarily involves
+> a loss of information when converting sound from analogue to digital. However,
+> given a high enough value for the sampling rate and bit-depth, the differences
+> are imperceptible to the human ear.

zk/SQLite.md

@@ -23,3 +23,37 @@ skip without throwing a constraint error.
 ```sql
 INSERT OR IGNORE INTO table_name (value) VALUES (:value)
 ```
+
+## exec and fetchall
+
+For `CREATE`, `INSERT`, `UPDATE`, `DELETE` operations it is sufficient to simply
+use `execute` to carry out the operations:
+
+```py
+cursor = connection.cursor()
+cursor.execute(sql)
+```
+
+For `SELECT` operations, you must add a return statement that uses `fetchall`:
+
+```py
+sql = "SELECT * FROM table"
+cursor = connection.cursor()
+cursor.execute(sql)
+return cursor.fetchall()
+```
+
+## SELECT response data type
+
+A `SELECT` operation returns a [list](Lists_in_Python.md) of
+[tuples](Tuples_in_Python.md) where each entry in the tuple is a returned field.
+
+For example:
+
+```py
+entries_sql = "SELECT title, size FROM entries"
+
+entries_response = cursor.execute(entries_sql)
+print(cursor.fetchall())
+# [('Lorem ipsum', 127), ('Dolar sit', 4231)]
+```

zk/Type_hinting.md

@@ -63,6 +63,35 @@ We could then use it thus:
 def parse_articles() -> list[ArticleInfo]:
 ```
 
+### Explicit type construction
+
+Sometimes, simply asserting that custom type will be returned by a function is
+not sufficient to pass the type checks. In these cases you need to explicitly
+construct the type within the function.
+
+For example this generates an error as Python sees the `tags` type as
+`[Dictionary]`, even though it matches the type:
+
+```python
+class IGraphNode(TypedDict):
+    id: str
+    type: str
+
+```
+
+```py
+tags = [{"id": f"#{tag[0]}", "type": "tag"} for tag in tags]
+```
+
+So you have to explicitly generate the type like this:
+
+```python
+tags = [IGraphNode(id=f"#{tag[0]}", type="tag") for tag in tags]
+```
+
+Then you will be able to type the return of the function as
+`-> list[IGraphNode]`
+
 ## Optional types
 
 `Optional` can be used to indicate that a variable can be `None` or the

zk/Working_with_JSON_in_Python.md

@@ -1,5 +1,4 @@
 ---
-id: mjia
 tags: [python, JSON]
 created: Tuesday, June 25, 2024
 ---
@@ -20,8 +19,13 @@ Will error if the input string is not properly formatted JSON. This will be
 Take a JSON-formatted dictionary and convert it into a string. The reverse of
 `json.loads()` and equivalent to `JSON.stringify()` in JavaScript.
 
-## JSON errors
+## `json.dump()`
 
-The `.loads()` and `.parse()` methods will throw an error if the input string is
+Not to be confused with the above. Output a Python dictionary as JSON, for
+instance to create a `.json` file:
 
-## Related notes
+```py
+data = { "key": "value"}
+with open("some/directory/output.json", "w") as f:
+    json.dump(data, f, indent=4)
+```

zk/dfsdfdf/Welcome.md

@@ -0,0 +1,5 @@
+This is your new *vault*.
+
+Make a note of something, [[create a link]], or try [the Importer](https://help.obsidian.md/Plugins/Importer)!
+
+When you're ready, delete this note and make the vault your own.

zk/eolas testg/Welcome.md

@@ -0,0 +1,5 @@
+This is your new *vault*.
+
+Make a note of something, [[create a link]], or try [the Importer](https://help.obsidian.md/Plugins/Importer)!
+
+When you're ready, delete this note and make the vault your own.