Support for 24 bit stereo audio at 96 kHz on i2s bus

[LBB]

Hi,

I would like to know whether 24 bit stereo audio at 96 kHz is supported on the nRF52840 in i2s slave mode using an external master clock source.

Using the internal clock it doesn't seem possible to achieve the necessary clock accuracy; please correct me if I used the clock table wrongly.

Thanks and regards.

[haakonsh]

Hey Luigi,

Max sample rate is 48kHz for stereo. See table below of the valid configurations:

MCK = 32MHz / Div		LRCK [kHz]
Div	MCK [kHz]	Ratio 32	Ratio 48	Ratio 64	Ratio 96	Ratio 128	Ratio 192	Ratio 256	Ratio 384	Ratio 512
2	16 000								41.67	31.25
3	10 667							41.67	27.78	20.83
4	8 000						41.67	31.25	20.83	15.63
5	6 400						33.33	25.00	16.67	12.50
6	5 333					41.67	27.78	20.83	13.89	10.42
8	4 000				41.67	31.25	20.83	15.63	10.42	7.81
10	3 200				33.33	25.00	16.67	12.50	8.33	6.25
11	2 909			45.45	30.30	22.73	15.15	11.36	7.58	5.68
15	2 133		44.44	33.33	22.22	16.67	11.11	8.33	5.56	4.17
16	2 000		41.67	31.25	20.83	15.63	10.42	7.81	5.21	3.91
21	1 524	47.62	31.75	23.81	15.87	11.90	7.94	5.95	3.97	2.98
23	1 391	43.48	28.99	21.74	14.49	10.87	7.25	5.43	3.62	2.72
30	1 067	33.33	22.22	16.67	11.11	8.33	5.56	4.17	2.78	2.08
31	1 032	32.26	21.51	16.13	10.75	8.06	5.38	4.03	2.69	2.02
32	1 000	31.25	20.83	15.63	10.42	7.81	5.21	3.91	2.60	1.95
42	762	23.81	15.87	11.90	7.94	5.95	3.97	2.98	1.98	1.49
63	508	15.87	10.58	7.94	5.29	3.97	2.65	1.98	1.32	0.99
125	256	8.00	5.33	4.00	2.67	2.00	1.33	1.00	0.67	0.50
Bit width	Allowed ratios
8	ALL
16	32 64 128 256 512
24	48 96 192 384

Cheers,

Håkon.

[LBB]

Hi Håkon,

thanks for the prompt reply.

This table seems to be strictly related to the clocks that the nRF52840 can generate with the onboard 32 MHz master clock.

Do the same limitations apply to the case in which the clock information is provided by the external amplifier and the nRF52840 is an i2s slave?

Thanks.

Cheers,

Luigi

[haakonsh]

Yes, max sample rate is 48KHz in any configuration. 

[jick]

HI Håkon,

I notice you said the max sample rate is 48KHz in any configuration,which makes me confused.

when MCK is 16MHz and ratio is 32,the max sample rate is 500KHz.But why no set?

Is there any relationship between Div and ratio?

[haakonsh]

You can try and see if it works, but I doubt it. We do not test for it, and therefore it's out of spec.