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Cut off frequency of DM816X DSP AAC encorder

hb chen
Expert 2640 points

Dear Experts,

My environment: DM8168/SDK Version: VCSDK(based on DVRRDK 2.8).

In my platform, I encoded alsa pcm audio data to AAC by RPE method. ( linux alsa audio in -> rpe -> dsp aac encode)

I check the cut off frequency of AAC encoded stream, it is 15KHz. (Frequency of original audio is over 20KHz).

Can I adjust the cut off frequency of DSP AAC encorder?

thx

HB

  • 0
    TI__Guru* 80190 points
    Hello,

    If I understand you right there is combination between sampling frequency and the bitrate.
    You could check thee AAC encoder user guide page 61.
    You could check page 18 for what the AAC encoder supports.

    BR
    Margarita
  • 0 in reply to Margarita Gashova
    Expert 2640 points
    Dear Margarita,

    I check my own document.
    AAC_LC_Encoder_C674x_UserGuide.pdf. Literature Number: SPRUHB5 September 2011.
    Page 61 is Frequently Asked Questions.
    Page 18 is Supported Services and Features.

    But I cannot find out the answers.

    My sampling frequency is 48kHz, bitrate setting is 128kbps. Stereo.
    Under this setting, can I reserve more high frequency component when perform DSP AAC encoding?
    For example, currently, AAC cut off frequency under my testing is 15KHz.
    If I want to keep 48KHz, stereo, and 128kbps, can I adjust this cut off frequency to 20KHz?

    thx ~

    HB
  • 0 in reply to hb chen
    TI__Guru* 80190 points
    Hello,

    For stereo the 48 000 and 44 100 Hz the min and the max bitrate is 80 000 up to 320 000 bps.

    -Supports input sampling frequencies from 16 kHz to 48 kHz for mono and stereo input files.
    -Supports input sampling frequencies from 32 kHz to 48 kHz for multichannel input files.



    BR
    Margarita
  • 0 in reply to Margarita Gashova
    TI__Mastermind 30480 points

    Hi HB,

    There is no configuration in AAC encoder for modifying cut-off frequency.

    since this is LC encoding, band truncation is expcted. With HEv1 or HEv2 encoding, you will be able to get full frequency range.

    Ramprasad

  • 0 in reply to Ramprasad
    Expert 2640 points

    Dear Ramprasad,

    Does TI have any document that discussed about this symptom?

    In my experimental as below figure (Left: encoded AAC stream, Right: Original PCM data), cut off at 15KHz is very obviously.

    Is it normal situation on DM8148 C6XDSP AAC encorder?

    Do I set wrong parameters to cause this situation or can I improve this situation?

    48KHZ, 128Kbps is given condition, I cannot change it.

    thx

    HB