snd_pcm_hw_params_set_channels (dev, params, ctx->channels);
if (snd_pcm_hw_params (dev, params) < 0) {
snd_pcm_hw_params_free (params);
snd_pcm_hw_params_set_channels (dev, params, ctx->channels);
if (snd_pcm_hw_params (dev, params) < 0) {
snd_pcm_hw_params_free (params);