#90 Installable FIR

[Guido Fragiacomo]

Subject: Questions regarding custom Installable FIR filters and sample rates in foo_input_sacd
Hello Maxim,
I have a few questions about configuring Installable low-pass FIR filters:

1. Does the design sampling frequency of the Installable FIR filter need to match the one selected in the "Samplerate" box? i.e. the FIR filter is applied to the PCM stream at the selected samplerate after the conversion from SACD/DSD?
2. I might be missing something, as the filters available in the subfolder can be loaded without any reference to a specific samplerate. Is this related to the decimation, and what exactly is its function here?
3. Additionally, after using foo_input_sacd, I use SoX to resample all PCM files to 96 kHz. Since SoX already applies a very steep linear-phase low-pass filter, does it make sense to use a custom installable
   filter in foo_input_sacd? I suppose it might, specifically for handling native 96 kHz files, what do you think?

Thank you for your help!

[Maxim V.Anisiutkin]

1. No, it doesn't. You just set decimation for this installable FIR. If decimation is set to 'Auto' it is determined as the rounding to 8, 16, 32, 64, etc. of filter length divided by 10. If decimation is not enough to get the output PCM frequency further PCM->PCM decimators are applied.
2. These filters can lower DSD frequency up to 64 times. Cutoff frequencies are related to DSD64 source.
3. No, it doesn't. But some people don't like neither Multistage, nor Direct filtering. So, option #3 (DIY:) is introduced.

[Guido Fragiacomo]

Maxim thank you for your quick response
Regards
Guido