One method to produce pure heralded single photons (HSP) when using the optical process of spontaneous parametric down-conversion (SPDC) is by modifying the joint spectrum of the photon pairs by means of spectral filters. In this work, we characterize the dependence, with the bandwidth of such filters, of the spectral purity and heralding efficiency of the HSP generated in a bulk SPDC. The values we report for the purity and heralding efficiency are obtained from measurements of the joint spectrum. Our results are in agreement with the theoretical model that predicts a trade-off between the purity and heralding efficiency, and they complement similar measurements that have been done for HSP produced by other types of sources.