Figure 1 - Part of the IPA consonant chart. Click here to view the entire chart.
Linguists classify the speech sounds used in a language into a number of abstract categories called phonemes. American English, for example, has about 41 phonemes as listed below, although the number varies according to the dialect of the speaker and the system of the linguist doing the classification. Phonemes are abstract categories which allow us to group together subsets of speech sounds. Even though no two speech sounds, or phones, are identical, all of the phones classified into one phoneme category are similar enough so that they convey the same meaning.
Phonemes can be classified into the following broad categories:
In this list above we used letters from the spelling of each word to point out which speech sound was meant. However, English spelling is not phonetic, as we all know. Phoneticians have developed a set of symbols which represent speech sounds not only for English, but for all existing spoken languages. The International Phonetic Alphabet (IPA) is recognized as the international standard for the transcription of phonemes in all of the world's languages. Since the IPA is not easily processed by computer, here at the CSLU we use an IPA-like ASCII symbol set called Worldbet. Click here to see a full chart of the IPA and Worldbet symbols commonly used for transcribing American English along with spectrograms illustrating each symbol pair.
For a more detailed account of the speech sounds of the world and their classification, our favorite text is A Course in Phonetics by Peter Ladefoged, one of the world's foremost linguists. His work Elements of Acoustic Phonetics is a deeper look at the connection between linguistics and acoustics. Click here for a list of useful texts on subjects touching spectrogram reading.
There is one more concept which it is important for a would-be spectrogram reader to understand, and that is the notion of formants.
Figure 2 - Part of the IPA vowel chart. Click here to view the entire chart.