Switching Supply Noise Filter for Audio Circuit
In general an SMPS generates a lot of switching noise.
However, most SMPSes use a switching frequency above 50 kHz as a lower frequency
would be inefficient.

An SMPS can generate lower frequency components depending on its design and in particular the amount of current it has to supply. Many SMPSes switch continuously at the same frequency. However some SMPSes go into a pulsed mode (PFM: pulsed frequency modulation) when the load draws only a low current. This is done to improve efficiency at low loads. The pulsed frequency can be in the kHz range, so every 100 us - 1ms there will be a short burst of 100 kHz. This you might want to avoid in your application. If the PFM mode of your SMPS is a problem then you might be able to work around it by drawing more power from it.

Another way to suppress the switching noise is to use linear regulators whith high supression in the desired frequency range.