Author:

• Name: Pierre-Philippe Coupard
  Location: US - United States of America (United States)

To build:

    make

To use:

    ./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” for help.

Try:

    ./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 and guidelines 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

    ./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 for example (sox is the Swiss army knife of Unix audio tools). The command:

    ./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 and a bad gramophone, 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 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 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.

Primary files

• coupard.c - entry source code
• Makefile - entry Makefile
• coupard.orig.c - original source code
• try.sh - script to try entry

Secondary files

• 2001_coupard.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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