Spectrograms are used for time-frequency analysis and as preprocessing for signal classifiers and other algorithms. The conventional spectrogram is a tapered short-time Fourier transform, equivalent to a bank of bandpass filters. The taper defines filter-bank characteristics such as bandwidth and sidelobe levels. Although the conventional spectrogram uses minimal computational resources, its design requires a compromise between resolution and interference suppression. Adaptive spectrogram algorithms adjust the filter-bank based on incoming data, thereby allowing different bandwidth/sidelobe trade-offs at each frequency and time. Adaptation can simultaneously improve tonal resolution and reveal quiet sources but typically costs substantially more to implement. This paper presents an adaptive spectrogram designed for applications with limited computational resources, e.g., autonomous vehicles. The performance weighted blended (PWB) spectrogram combines the output of a set of conventional filter-banks designed with different tapers. By adapting its blend weights at each frequency and time, the new algorithm separates loud closely spaced tones and identifies quiet signals. Because it relies on conventional filter-banks, the PWB spectrogram requires significantly less computation than other adaptive algorithms that require expensive matrix computations. Analysis of underwater glider data demonstrates the algorithm's ability to reveal a quiet chirp signal in the presence of vehicle self-noise.