Fiio m21 settings sq car audio

[MikeR89]

Hi everyone,

I’m new to posting here, although I’ve been reading along on the forum for quite a while. I’ve already learned a lot from the discussions, so thanks to everyone who shares their knowledge here.

I have a question about the best settings for my FiiO M21, specifically regarding the low pass filter and DAC DRE settings.

My setup is as follows:
I’m using the FiiO M21 via Bluetooth (aptX HD) into a Helix DSP Pro MK3, which has the BT module with aptX HD support. From there, the signal goes into my active system.

The reason I’m asking is that my Bliesma T25B tweeters seem to roll off quite quickly in the high frequencies — already around 16 kHz. I’m trying to figure out whether this could be related to the FiiO settings (LPF or DRE), or whether I should be looking elsewhere in the chain. ( Previous tweeters in the same location extended up to 20 kHz when using my iPhone )

So my questions are:

• Which low pass filter setting would be most appropriate in this situation?
• Should DAC DRE be enabled or disabled when using Bluetooth aptX HD into an external DSP?
• Could these settings realistically influence high-frequency roll-off, or is that unlikely when using BT digital output?

Any insights or experiences with a similar setup would be greatly appreciated.

Thanks in advance!