Spectrograms (sometimes called sonograms or sonagrams) are visual representations of sound: graphs of frequency across time. Spectrograms are read from left to right; lower frequencies (lower-pitched sounds) are near the bottom, and higher frequencies (higher-pitched sounds) are near the top. It takes practice and skill to read spectrograms well, but if you are serious about studying bird sounds, you must learn to read them. Trust me on this.
On these pages you will find a step-by-step tutorial in learning to read spectrograms, which is at the same time a step-by-step tutorial in how to listen to and describe bird sounds.
Lesson one: Pitch and Inflection
Lesson two: Musicality
Lesson three: Noise
Lesson four: Trills and Beats
Lesson five: Nasality
Lesson six: Polyphony
For those who want more information on spectrograms, check out these posts I wrote to expand on the knowledge in the tutorial pages above: