Azure Cognitive Speech-to-text DetailedSpeechRecognitionResult is not detecting explicit punctuation

What you are observing is by design. In most circumstances it not necessary or even helpful to inspect the details of recognized speech result. It looks like you have misinterpreted how to use the details.

You don’t realise it but your example of detecting "new line" or "newline" as a key phrase and interpreting that as a request to inject a line feed into the output is the very same process at work.

For puntuation to be detected in the speech, the first thing that the classifier must do is resolve the words. It is only after the word has been resolved that the service can post process the results to classify the word as a natural word or punctuation.

The process is a bit like this:

1. Detected the word "comma" with high confidence
2. If the punctuation setting is set to explicit, then Is the word on its own or at the end of a recognized sequence that was followed by a pause
3. If yes, then interpret it as "," and not "comma"

For this reason it is important to understand that when the punctuation setting is set to explicit, the punctuation must be isolated out of the normal sentence cadence of the spoken text.

Read this as a sentence with a constant pace without punctuation:

this is a sentence that doesn’t have a comma or a full stop but an exclamation mark would look nice

If you read fast and fluent enough, there should be no punctation in the output, even if the words were recognized with high confidence. To get punctuation into the same text, you actually need to read this script:

This is a sentence that doesn’t have a comma.
Comma.
Or a fullstop.
Comma.
But an exclamation mark would look nice.
exclamation mark.

 This is a sentence that doesn't have a comma , or a full stop , but an exclamation mark would look nice !

The per-word analysis for my test looks like this:

Notice that the words representing the punctuation all have a high confidence rating, but in the output not all of the words were actually interpreted as punctuation. This might be clearer in this screenshot where I have highlighted two commas that are in the output, but are correctly identified as words:

In this screenshot, the panel on the left is populated with e.Result.Text and the panel on the right with the Word and Confidence.

DetailedSpeechRecognitionResult.Words
Returns the Word level timing result list.

The Words list is designed to be used to map the recognised word back to a specific offset and duration in the audio file that was submitted for analysis. You would use this information when testing and training the model or if you wanted to display the text as sub-titles for an audio or video clip. Punctuation is not shown at this level, it is purely about timing only, all it has done is literally transcribed the spoken audio into English vocabulary. It is the responsibility of other analytical functions to use this information to determine which detected words might represent punctuation or to determine context or sentiment.

FWIW this is my Recognized event handler:

recognizer.Recognized += (s, e) =>
{
    // Checks result.
    if (e.Result.Reason == ResultReason.RecognizedSpeech)
    {
        Console.WriteLine($"RECOGNIZED: Text={e.Result.Text}");
        string text = e.Result.Text;
        if (e.Result.Text.ToLower().Equals("new line") || e.Result.Text.ToLower().Equals("newline"))
            text = Environment.NewLine;

        // update the left textbox
        this.BeginInvoke(SetText, textBox1, text); 

        var detailedResults = e.Result.Best();
        if (detailedResults != null && detailedResults.Any())
        {
            var bestResults = detailedResults?.ToList()[0];
            foreach (var word in bestResults.Words)
            {
                double perc = word.Confidence * 100;
                // update the right textbox
                this.BeginInvoke(SetText, textBox2, $"{word.Word} [{word.Confidence:p2}] " + Environment.NewLine);
            }
        }
    }
    else if (e.Result.Reason == ResultReason.NoMatch)
    {
        Console.WriteLine($"NOMATCH: Speech could not be recognized.");
    }
};
...
delegate void SetTextDelegate(TextBox textBox, string text);
private SetTextDelegate SetText = delegate (TextBox textbox, string text)
{
    textbox. Text += " " + text;
};