Functions

This section lists all the API functions of the SSRC module and explains their parameters.

SSRC_GetNrSamples

Prototype:

SSRC_ReturnStatus_en SSRC_GetNrSamples
   (SSRC_NR_SAMPLES_MODE_en  Mode,
    SSRC_Params_t*           pSSRC_Params );

Description:

This function retrieves the number of samples or sample pairs for stereo used as an input and as an output of the SSRC module.

Name

Type

Description

Mode

SSRC_NR_SAMPLES_MODE_en

There are two modes:
- SSRC_NR_SAMPLES_DEFAULT: In this mode, the function returns the number of samples for 40 ms blocks
- SSRC_NR_SAMPLES_MIN: the function returns the minimal number of samples supported for this conversion ratio. The SSRC_Init function accepts each integer multiple of this ratio.
Formula: blocksize (ms) = 1/gcd(Fs_In,Fs_Out)

pSSRC_Params

SSRC_Params_t*

Pointer to the instance parameters. The application fills in the values of the input sample rate, the output sample rate, and the number of channels. Based on this input, the SSRC_GetNrSamples fills in the values for the number of samples for the input and the output audio stream.

Returns:

SSRC_OK

When the function call succeeds.

SSRC_INVALID_FS

When the requested input or output sampling rates are invalid.

SSRC_INVALID_NR_CHANNELS

When the channel format is not equal to LVM_MONO or LVM_STEREO.

SSRC_NULL_POINTER

When pSSRC_Params is a NULL pointer.

SSRC_INVALID_MODE

When mode is not a valid setting.

Note: The SSRC_GetNrSamples function returns the values from the following tables. Instead of calling the SSRC_GetNrSamples function, use the values from these tables directly.

Sample rate

Nr of samples

8000

320

11025

441

12000

480

16000

640

22050

882

24000

960

32000

1280

44100

1764

48000

1920

In/Out

8000

11025

12000

16000

22050

24000

32000

44100

48000

8000

1
1

320
441

2
3

1
2

160
441

1
3

1
4

80
441

1
6

11025

441
320

1
1

147
160

441
640

1
2

147
320

441
1280

1
4

147
640

12000

3
2

160
147

1
1

3
4

80
147

1
2

3
8

40
147

1
4

16000

2
1

640
441

4
3

1
1

320
441

2
3

1
2

160
441

1
3

22050

441
160

2
1

147
80

441
320

1
1

147
160

441
640

1
2

147
320

24000

3
1

320
147

2
1

3
2

160
147

1
1

3
4

80
147

1
2

32000

4
1

1280
441

8
3

2
1

640
441

4
3

1
1

320
441

2
3

44100

441
80

4
1

147
40

441
160

2
1

147
80

441
320

1
1

147
160

48000

6
1

640
147

4
1

3
1

320
147

2
1

3
2

160
147

1
1

Parent topic:Functions

SSRC_GetScratchSize

Prototype:

SSRC_ReturnStatus_en SSRC_GetScratchSize
   (SSRC_Params_t*    pSSRC_Params,
    LVM_INT32*        pScratchSize );

Description:

This function retrieves the scratch size for a given conversion ratio and for given buffer sizes at the input and at the output.

Name

Type

Description

pSSRC_Params

SSRC_Params_t*

Pointer to the instance parameters. All members should have a valid value.

pScratchSize

LVM_INT32*

Pointer to the scratch size. The SSRC_GetScratchSize function fills in the correct value (in bytes).

|

Returns:

SSRC_OK

When the function call succeeds.

SSRC_INVALID_FS

When the requested input or output sampling rates are invalid.

SSRC_INVALID_NR_CHANNELS

When the channel format is not equal to LVM_MONO or LVM_STEREO.

SSRC_NULL_POINTER

When pSSRC_Params or pScratchSize is a NULL pointer.

SSRC_WRONG_NR_SAMPLES

When the number of samples on the input or on the output are incorrect.

Parent topic:Functions

SSRC_Init

Prototype:

SSRC_ReturnStatus_en SSRC_Init
   (SSRC_Instance_t* pSSRC_Instance,
    SSRC_Scratch_t*  pSSRC_Scratch,
    SSRC_Params_t*   pSSRC_Params,
    LVM_INT16**      ppInputInScratch,
    LVM_INT16**      ppOutputInScratch);

Description:

The SSRC_Init function initializes an instance of the SSRC module.

Name

Type

Description

pSSRC_Instance

SSRC_Instance_t*

Pointer to the instance of the SSRC. This application must allocate the memory before calling the SSRC_Init function.

pSSRC_Scratch

SSRC_Scratch_t*

Pointer to the scratch memory. The pointer is saved inside the instance and is used by the SSRC_Process function. The application must allocate the scratch memory before calling the SSRC_Init function.

pSSRC_Params

SSRC_Params_t*

Pointer to the instance parameters.

ppInputInScratch

LVM_INT16**

The SSRC module can be called with the input samples located in scratch. This pointer points to a location that holds the pointer to the location in the scratch memory that can be used to store the input samples. For example, to save memory.

ppOutputInScratch

LVM_INT16**

The SSRC module can store the output samples in the scratch memory. This pointer points to a location that holds the pointer to the location in the scratch memory that can be used to store the output samples. For example, to save memory.

Returns:

SSRC_OK

When the function call succeeds.

SSRC_INVALID_FS

When the requested input or output sampling rates are invalid.

SSRC_INVALID_NR_CHANNELS

When the channel format is not equal to LVM_MONO or LVM_STEREO.

SSRC_NULL_POINTER

When pSSRC_Params or pScratchSize is a NULL pointer.

SSRC_WRONG_NR_SAMPLES

When the number of samples on the input or on the output are incorrect.

SSRC_ALIGNMENT_ERROR

When the instance memory or the scratch memory is not 4 bytes aligned.

Parent topic:Functions

SSRC_SetGains

Prototype:

SSRC_ReturnStatus_en SSRC_SetGains
   (SSRC_Instance_t* pSSRC_Instance,
    LVM_Mode_en      bHeadroomGainEnabled,
    LVM_Mode_en      bOutputGainEnabled,
    LVM_INT16       OutputGain);

Description:

This function sets headroom gain and the post gain of the SSRC. The SSRC_SetGains function is an optional function that should be used only in rare cases. Preferably, use the default settings.

Name

Type

Description

pSSRC_Instance

SSRC_Instance_t*

Pointer to the instance of the SSRC.

bHeadroomGainEnabled

LVM_Mode_en

Parameter to enable or disable the headroom gain of the SSRC. The default value is LVM_MODE_ON. LVM_MODE_OFF can be used if it can be guaranteed that the input level is below - 6 in all cases (the default headroom is -6 dB).

bOutputGainEnabled

LVM_Mode_en

Parameter to enable or disable the output gain. The default value is LVM_MODE_ON.

OutputGain

LVM_INT16

The value of the output gain. The output gain is a linear gain value. 0x7FFF is equal to +6 dB and 0x0000 corresponds to -inf dB. By default, a 3 dB gain is applied (OutputGain = 23197), resulting in an overall gain of -3 dB (-6 dB headroom +3 dB output gain).

Unit Q format Data Range Default value
Linear gain Q1.14 [0;32767] 23197

Returns:

SSRC_OK

When the function call succeeds

SSRC_NULL_POINTER

When pSSRC_Instance is a NULL pointer

SSRC_INVALID_MODE

Wrong value used for the bHeadroomGainEnabled or the OutputGainEnabled parameters.

SSRC_INVALID_VALUE

When OutputGain is out of the range [0;32767].

Parent topic:Functions

SSRC_Process

Prototype:

SSRC_ReturnStatus_en SSRC_Process
   (SSRC_Instance_t* pSSRC_Instance,
    LVM_INT16*       pSSRC_AudioIn,
    LVM_INT16*       pSSRC_AudioOut);

Description:

Process function for the SSRC module. The function takes pointers as input and output audio buffers.

The sample format used for the input and output buffers is 16-bit little-endian. Stereo buffers are interleaved (L1, R1, L2, R2, and so on), mono buffers are deinterleaved (L1, L2, and so on).

Name

Type

Description

pSSRC_Instance

SSRC_Instance_t*

Pointer to the instance of the SSRC.

pSSRC_AudioIn

LVM_INT16*

Pointer to the input samples.

pSSRC_AudioOut

LVM_INT16*

Pointer to the output samples.

Returns:

SSRC_OK

When the function call succeeds.

SSRC_NULL_POINTER

When one of pSSRC_Instance, pSSRC_AudioIn, or pSSRC_AudioOut is NULL.

Parent topic:Functions

SSRC_Process_D32

Prototype:

SSRC_ReturnStatus_en SSRC_Process_D32
   (SSRC_Instance_t* pSSRC_Instance,
    LVM_INT32*       pSSRC_AudioIn,
    LVM_INT32*       pSSRC_AudioOut);

Description:

Process function for the SSRC module. The function takes pointers as input and output audio buffers.

The sample format used for the input and output buffers is 32-bit little-endian. Stereo buffers are interleaved (L1, R1, L2, R2, and so on), mono buffers are deinterleaved (L1, L2, and so on).

Name

Type

Description

pSSRC_Instance

SSRC_Instance_t*

Pointer to the instance of the SSRC.

pSSRC_AudioIn

LVM_INT32*

Pointer to the input samples.

pSSRC_AudioOut

LVM_INT32*

Pointer to the output samples.

Returns:

|SSRC_OK|When the function call succeeds.| |SSRC_NULL_POINTER|When one of pSSRC_Instance, pSSRC_AudioIn, or pSSRC_AudioOut is NULL.|

Parent topic:Functions

Parent topic:Application programmers interface (API)