Supercapacitor Vs Battery Power
Both of these power sources provide super stable DC voltages at the currents required by audio devices. This stability is one of the key characteristics of a power supply driving any audio equipment but crucial for devices that handle very low voltage signals. Stability means not only preventing voltage sag when dynamic current is required but more importantly doing so without any fluctuation on the ground.
Digital audio transmission & processing is often done in distinct chunks (packets) & often required almost instantly. These gulps of current often happen with very high frequency timing. For instance, high speed USB data arrives in microframes of up to 1024 bytes (max) every 125uS. The amount of data in each microframe will vary & other control signals will also occur at different intervals. So any power supply being used in this situation needs to be immune to all these fluctuations in timing, current delivery. If not immune then the result is usually dynamic noise on the ground which has downstream effects on audio quality.
LiFePo4 batteries & supercapactitors are both capable of satisfying these requirements & the only difference between them appears to be the speed of the current delivery. High capacity supercapacitors often have a very low impedance (this value is a measure of the ability to deliver current quickly - the lower the impedance, the faster the current delivery). The LiFePO4 batteries have an internal impedance of <8mohm - the supercapacitors I use (Nesscap/Maxwell 350F ) have impedance <3.2mohm. This should mean that the supercapacitors can deliver current faster than the batteries. This seems to be borne out in the listening, supercapacitors appear to have slightly faster. However, pcb traces & wires will negate this impedance difference so perhaps the audible difference is due to some other factor?
Both batteries & supercapacitors are still unfazed & stable when delivering the needed current. This means no dynamic noise is created in the ground plane which ultimately affects the audibility