Brickworks > API documentation > bw_src_int

Integer-ratio IIR sample rate converter.

The multi-rate filtering approach was inspired by

M. Holters and J. D. Parker, "A Combined Model for a Bucket Brigade Device and its Input and Output Filters", 21st Intl. Conf. Digital Audio Effects (DAFx-18), Aveiro, Portugal, September 2018.

Module type: dsp

Version: 1.1.0

Requires:

```
typedef struct bw_src_int_coeffs bw_src_int_coeffs;
```

Coefficients and related.

```
typedef struct bw_src_int_state bw_src_int_state;
```

Internal state and related.

```
static inline void bw_src_int_init(
bw_src_int_coeffs * BW_RESTRICT coeffs,
int ratio);
```

Initializes `coeffs`

using the given resampling `ratio`

.

If `ratio`

is positive, then the sample rate of the output signal will be `ratio`

times the sample rate of the input signal, otherwise, if it is negative, then the sample rate of the output signal will be equal to the sample rate of the input signal divided by `-ratio`

.

`ratio`

must not be in [`-1`

, `1`

].

```
static inline float bw_src_int_reset_state(
const bw_src_int_coeffs * BW_RESTRICT coeffs,
bw_src_int_state * BW_RESTRICT state,
float x_0);
```

Resets the given `state`

to its initial values using the given `coeffs`

and the initial input value `x_0`

.

Returns the corresponding initial output value.

```
static inline void bw_src_int_reset_state_multi(
const bw_src_int_coeffs * BW_RESTRICT coeffs,
bw_src_int_state * BW_RESTRICT const * BW_RESTRICT state,
const float * x_0,
float * y_0,
size_t n_channels);
```

Resets each of the `n_channels`

`state`

s to its initial values using the given `coeffs`

and the corresponding initial input value in the `x_0`

array.

The corresponding initial output values are written into the `y_0`

array, if not `BW_NULL`

.

```
static inline size_t bw_src_int_process(
const bw_src_int_coeffs * BW_RESTRICT coeffs,
bw_src_int_state * BW_RESTRICT state,
const float * BW_RESTRICT x,
float * BW_RESTRICT y,
size_t n_in_samples);
```

Processes the first `n_in_samples`

of the input buffer `x`

and fills the output buffer `y`

using `coeffs`

, while using and updating `state`

.

The number of generated output samples will be `ratio`

times `n_in_samples`

if `ratio`

is positive, otherwise at most `n_in_samples`

divided by `-ratio`

and then rounded towards positive infinity.

`x`

and `y`

must point to different buffers.

Returns the number of generated output samples.

```
static inline void bw_src_int_process_multi(
const bw_src_int_coeffs * BW_RESTRICT coeffs,
bw_src_int_state * BW_RESTRICT const * BW_RESTRICT state,
const float * BW_RESTRICT const * BW_RESTRICT x,
float * BW_RESTRICT const * BW_RESTRICT y,
size_t n_channels,
size_t n_in_samples,
size_t * BW_RESTRICT n_out_samples);
```

Processes the first `n_in_samples`

of the `n_channels`

input buffers `x`

and fills the `n_channels`

output buffers `y`

using `coeffs`

, while using and updating each of the `n_channels`

`state`

s.

The number of generated output samples in each output buffer will be `ratio`

times `n_in_samples`

if `ratio`

is positive, otherwise at most `n_in_samples`

divided by `-ratio`

and then rounded towards positive infinity.

A given buffer cannot be used both as an input and output buffer.

`n_out_samples`

is filled with the number of generated output samples for each output buffer, if not `BW_NULL`

.

```
static inline char bw_src_int_coeffs_is_valid(
const bw_src_int_coeffs * BW_RESTRICT coeffs);
```

Tries to determine whether `coeffs`

is valid and returns non-`0`

if it seems to be the case and `0`

if it is certainly not. False positives are possible, false negatives are not.

`coeffs`

must at least point to a readable memory block of size greater than or equal to that of `bw_src_int_coeffs`

.

```
static inline char bw_src_int_state_is_valid(
const bw_src_int_coeffs * BW_RESTRICT coeffs,
const bw_src_int_state * BW_RESTRICT state);
```

Tries to determine whether `state`

is valid and returns non-`0`

if it seems to be the case and `0`

if it is certainly not. False positives are possible, false negatives are not.

If `coeffs`

is not `BW_NULL`

extra cross-checks might be performed (`state`

is supposed to be associated to `coeffs`

).

`state`

must at least point to a readable memory block of size greater than or equal to that of `bw_src_int_state`

.

```
template<size_t N_CHANNELS>
class SRCInt {
public:
SRCInt(
int ratio);
void reset(
float x0 = 0.f,
float * BW_RESTRICT y0 = nullptr);
#ifndef BW_CXX_NO_ARRAY
void reset(
float x0,
std::array<float, N_CHANNELS> * BW_RESTRICT y0);
#endif
void reset(
const float * x0,
float * y0 = nullptr);
#ifndef BW_CXX_NO_ARRAY
void reset(
std::array<float, N_CHANNELS> x0,
std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr);
#endif
void process(
const float * BW_RESTRICT const * BW_RESTRICT x,
float * const * BW_RESTRICT y,
size_t nInSamples,
size_t * BW_RESTRICT nOutSamples = nullptr);
#ifndef BW_CXX_NO_ARRAY
void process(
std::array<const float * BW_RESTRICT, N_CHANNELS> x,
std::array<float * BW_RESTRICT, N_CHANNELS> y,
size_t nInSamples,
std::array<size_t, N_CHANNELS> * BW_RESTRICT nOutSamples = nullptr);
#endif
...
}
```

- Version
**1.1.0**:- Now using
`BW_NULL`

and`BW_CXX_NO_ARRAY`

.

- Now using
- Version
**1.0.0**:- Added
`bw_src_int_reset_state_multi()`

and updated C++ API in this regard. - Now
`bw_src_int_reset_state()`

returns the initial output value. - Added overloaded C++
`reset()`

functions taking arrays as arguments. `bw_src_int_lim_process()`

and`bw_src_int_lim_process_multi()`

now use`size_t`

to count samples and channels.- Added more
`const`

and`BW_RESTRICT`

specifiers to input arguments and implementation. - Moved C++ code to C header.
- Added overloaded C++
`process()`

function taking C-style arrays as arguments. - Fixed frequency response and improved speed.
- Removed usage of reserved identifiers.
- Clarified that the same buffer cannot be used for both input and output.
- Added debugging code.

- Added
- Version
**0.6.0**:- Removed dependency on bw_config.

- Version
**0.5.0**:- Added
`bw_src_int_process_multi()`

. - Added C++ wrapper.

- Added
- Version
**0.4.0**:- First release.