topic Re: ASRC use for downsampling in i.MX Processors

ASRC use for downsampling

j_paixao — Thu, 11 Jun 2020 14:46:46 GMT

Hello,

I'm today coming to the community with a question regarding the i.MX6ULL.

I would like to use the ASRC for downsampling a signal from 32kHz to 8kHz.

Unfortunately I am seeing some contradictions in the user manual and in the linux software documentation regarding this use.

Indeed in the reference manual Chapter 16.5 - Table 16-7 and figure 16-3:

There it shows the availability of post and pre-filters which can be set to support resampling from 32kHz to 8kHz.

While in the reference manual Chapter 16.1.1 it is mentioning that resampling from 32kHz to 8kHz is not supported:

Next to this on software level Linux is being used, there is an Alsa plugin in order to make use of the hardware resampler (imx-alsa-plugin -> http://sources.buildroot.net/imx-alsa-plugins/git/), in the documentation the following is mentionned (http://sources.buildroot.net/imx-alsa-plugins/git/doc/asrcrate.txt):

ASRC hardware can only support some fixed sample rates, don't make use it if you don't know which rates are in your cases. Input: 8000 16000 22050 32000 44100 48000 64000 88200 96000 176400 192000 Output: 32000 44100 48000 64000 88200 96000 176400 192000

This software documentation shows that resampling from 32kHz to 8kHz is not possible.

Anyone would have some experience with this ASRC module ?

Julien.

Re: ASRC use for downsampling

igorpadykov — Fri, 12 Jun 2020 05:45:01 GMT

Hi Julien

> I am seeing some contradictions in the user manual and in the linux software documentation regarding this use.
>Indeed in the reference manual Chapter 16.5 - Table 16-7 and figure 16-3:
>There it shows the availability of post and pre-filters which can be set to support resampling from 32kHz to 8kHz.
>This software documentation shows that resampling from 32kHz to 8kHz is not possible.

ASRC description in Reference Manual is general IP module description, while each processor

can have own restrictions. Unfortunately for i.MX6ULL resampling from 32kHz to 8kHz is not possible

For example below i.MX35 description which shows that for this processor this is possible.

Best regards
igor
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Re: ASRC use for downsampling

j_paixao — Fri, 12 Jun 2020 06:44:45 GMT

Hi Igor,

This clarifies the situation, thanks for your answer :smileyhappy:

Best regards,

Julien.