Two instruments can play the same pitch and still sound distinctly different. This tone colour is often called timbre. Naming the instrument is only one way into listening. It can be equally useful to describe what the sound does: does it begin softly or sharply, remain steady, become rougher or fade quickly? These observations remain possible even when the source is unknown.
Notice the beginning of a note
Choose a passage where an instrument enters without dense accompaniment. Attend first to the onset. A plucked note may have a clearly defined beginning, while another sound swells gradually. This does not securely identify the instrument. Playing technique and processing can alter a familiar impression.
Next, listen to the course of the sound after its entrance. Does it stay even, change intensity or develop an audible fluctuation? Finally, consider the ending. Does it stop clearly or leave a decay in the room? Three short descriptions can be more precise than a single adjective such as warm, which different listeners may use differently.
Compare similar registers
Two short passages in roughly similar registers and at comfortable, comparable volume make a useful comparison. Contrasting a very low note with a very high one mixes pitch and timbre in the impression. That is legitimate, but answers a different question. Keep other factors reasonably consistent when investigating the character of the sound.
Yamaha's instrument guide uses the acoustic guitar to explain the body's involvement in producing sound. A recording nevertheless includes more than the instrument: performance, room and recording choices also contribute. A muted sound does not prove that a particular construction must always sound muted.
Make descriptions useful to another listener
When listening with somebody else, each offer an adjective followed by the audible property behind it. Bright might refer to prominent high components; sharp might mean a sudden onset. The explanation makes the statements comparable. You do not need identical vocabulary if the observation behind each word is clear.
Then try a passage with several instruments. Can you hear a melody being handed over even when the pitch remains similar? Which change makes the transfer noticeable? The exercise is not a comprehensive instrument-identification quiz. It helps distinguish relationships within a recording, even when the ensemble is only established later through reliable credits. Naming what you hear first also reduces the temptation to hear only what you expect from an instrument label.