According to AK4497 | News | AKM - Asahi Kasei Microdevices [RWD] , you can choose between six types of 8 times oversampling filter, although the datasheet also mentiones an EXDF (external digital filter) mode that bypasses the internal filter:
"Sound Color Six Types, 32-bit 8-fold Digital Filters
- Short Delay Sharp Roll-off, GD=6.25/fs
- Short Delay Slow Roll-off, GD=5.3/fs
- Sharp Roll-off
- Slow Roll-off
- Super Slow Roll-off
- Low-dispersion Short Delay".
The sigma-delta modulators (see the block diagram on page 4 of https://www.akm.com/akm/en/file/datasheet/AK4497EQ.pdf ) will need a much higher oversampling to work well. Presumably this is the bit that works at 256 times the input sample rate.
"Sound Color Six Types, 32-bit 8-fold Digital Filters
- Short Delay Sharp Roll-off, GD=6.25/fs
- Short Delay Slow Roll-off, GD=5.3/fs
- Sharp Roll-off
- Slow Roll-off
- Super Slow Roll-off
- Low-dispersion Short Delay".
The sigma-delta modulators (see the block diagram on page 4 of https://www.akm.com/akm/en/file/datasheet/AK4497EQ.pdf ) will need a much higher oversampling to work well. Presumably this is the bit that works at 256 times the input sample rate.
Thank you for the replies.
I am aware of the auto-detect and the filters, however, right now I have no way to change the default settings.
I am sending a 44.1 kHz signal, via USB, from the PC to the XMOS USB to I2S converter. The I2S signal is then converted by the AK4497 at the default settings. I'd like to know if, as part of this process, the AK4497 upsamples higher than 44.1.
I can upsample in Windows to 24/192 but I don't want upsample in Windoes if the DAC is upsampling to a higher level.
I am aware of the auto-detect and the filters, however, right now I have no way to change the default settings.
I am sending a 44.1 kHz signal, via USB, from the PC to the XMOS USB to I2S converter. The I2S signal is then converted by the AK4497 at the default settings. I'd like to know if, as part of this process, the AK4497 upsamples higher than 44.1.
I can upsample in Windows to 24/192 but I don't want upsample in Windoes if the DAC is upsampling to a higher level.
Looking at pages 86 and further of the datasheet, when the AK4497 is under register control, the default is internal digital filter, no automatic sample rate detection, short delay filter, fast roll-off (that is, no slow roll-off and no super-slow roll-off). In fact you also find that filter setting in Table 28 on page 61. Under hardware control, it depends on what voltages are applied to the control pins.
So all in all, under register control. by default the signal goes through an eight times oversampling digital filter and then it is oversampled further by the sigma-delta modulator.
So all in all, under register control. by default the signal goes through an eight times oversampling digital filter and then it is oversampled further by the sigma-delta modulator.
Thank you! I will turn off oversampling in Foobar and output a 44.1kHz signal.
Today I should receive from DIYINHK one of the cheapo "1.3" OLED and rotary encoder volume control PCB" and a newer XMOS USB to I2S converter that will allow me to change the filters in the AK4497.
I'm not sure what to expect from the filters but I am looking forward to finding out.
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