ioccc/2001/coupard/README.md

## To build:

``` <!---sh-->
    make
```


## To use:

``` <!---sh-->
    ./coupard
```

**NOTE**: the author notes that you might want to convert the sound formats. For
this you can use `SoX`. If you do not have this installed then see the
FAQ on "[using entries that require sound](../../faq.html#sox)"
for help.



## Try:

``` <!---sh-->
    ./try.sh
```


## Judges' remarks:

You may need to run this a few times to understand exactly what is
being said.  You might even need to look somewhere on your desktop,
your arm or the wall for confirmation.


## Author's remarks:

Past years' IOCCC entries do many marvellous things in small packages,
such as console utilities, games, math, languages or even X
applications.  But they all have one thing in common (despite being hard
to read obviously): when they interact with the user, they only
*display* things, i.e. they display either text or drawings.

So, for a change, this program titillates the sense of hearing instead
of sight: this program is a self-contained speech synthesizer that
tells the current time through the computer's sound card - in just under
2 Kb of source code !

In the 2001 IOCCC [rules](../rules.txt) and
[guidelines](../guidelines.txt) documents, there is no mention of
what is or isn't acceptable regarding audio I/O, but it is mentioned
that hardware-specific and/or non-portable programs are not welcome. So,
in order to do audio and satisfy those requirements, the format required
by `/dev/audio` has been chosen: `/dev/audio` is a rather ancient
fixed-format audio interface that is supported by the majority of Unices
that can do sound, as a lowest-denominator sound I/O interface.

### Program usage

To listen to what the program says directly, invoke

``` <!---sh-->
    ./coupard > /dev/audio
```

The program then speaks out something like

```
    The time is HH hours MM minutes SS seconds
```

in military time (24 hours). Of course, you need to have permissions
to write to `/dev/audio`, have your sound card enabled, the volume up,
the speakers connected ... :-)

If you want to convert the audio output of the program into another audio
format, you can pipe it to [SoX](https://en.wikipedia.org/wiki/SoX) for example
(`sox` is the Swiss army knife of Unix audio tools). The command:

``` <!---sh-->
    ./coupard | sox -c1 -r8000 -tub - -c2 -r44100 -twav test.wav
```

converts the output of the program into a 44.1KHz stereo .WAV
file and saves it into `test.wav`.

The output format of the program is 8KHz, unsigned 8-bit samples.

**NOTE**: the program's return code is meaningless.


### Audio quality

The quality of the sound produced by the program is cross between a
[yogurt-pot-and-string
telephone](https://en.wikipedia.org/wiki/Tin_can_telephone) and a bad
[gramophone](https://en.wikipedia.org/wiki/Phonograph), i.e. the S/N ratio is
very low and the signal's top frequency is very low as well.  This is because
the audio is stored internally at a sampling rate of 4KHz (the [Nyquist
frequency](https://en.wikipedia.org/wiki/Nyquist_frequency) is only 2KHz) with
only 4-bit samples (adding 24db of quantization noise to an already poor
signal).

In short, you might have to listen twice to understand what the
program is saying. 2048 bytes including the sound generation program
doesn't leave much room for audio quality ;-)


### Speech generation

Only 9 phonemes are used to generate the speech. Beside the limited
number of words the program has to generate (66 words), the low sound
quality is actually exploited to take liberties with certain
consonants (for example, `s` and `f` sound very much the same at 4KHz,
so they can be merged into one phoneme). Because the
[psychoacoustic](https://en.wikipedia.org/wiki/Psychoacoustics)
context around those phonemes is just sufficient, the words can be
interpreted correctly most of the time despite the fact that they are
pronounced quite wrongly.

Internally, a table is used to generate most of the words, and
composite words such as "thirty-five" are made up by the C code
externally.


### Data compression

Even at 4KHz / 4 bits, the weight of all the phoneme samples and the
word-to-phonemes table put together is over 1600 bytes, which is well
over 2048 bytes when encoded in a C string made of printable
characters.  Therefore, a compression method was needed that's both
efficient and with a decompressor that is implementable in the
shortest amount of code possible. GSM compression is very good, but
needs large psychoacoustic tables to regenerate the original
signal. Raw FFT spectral compression is efficient too, but the
decompression code can't be made small enough.

The best compression compromise was found using a simple Huffman
compressor, and encoding the compressed data by blocks of 13 bits in
pairs of printable ASCII characters: the raw data is compressed to
8465 bits, and the resulting C string is therefore about 1300
characters, which leaves just enough room for the decompressor with a
hard-coded Huffman tree, and the code that plays the phonemes in the
right order.


### Note on compiler warnings and lint

The program should build with `gcc -Wall -Werror -ansi`.  If the `-pedantic`
flag is used, gcc will complain about the length of the data string and the sign
of its type, and also the fact that `main()` returns with no value. The
confusion with the sign of the char type doesn't matter with the data string
because it's composed only of printable characters under 127.

When linting the program with `lclint`, it complains about a huge list
of things that, if corrected to make lint happy, would probably double
the size of the source code.


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