# freq
[](https://www.npmjs.com/package/tonal-freq)
[](https://www.npmjs.com/browse/keyword/tonal)
`tonal-freq` is a collection of functions to perform calculations related to frequencies.
This is part of [tonal](https://www.npmjs.com/package/tonal) music theory library.
## Usage
```js
var freq = require('tonal-freq')
freq.toFreq('A4') // => 440
freq.note(440) // => 'A4'
freq.noteAndDetune(320) // => ['C4', 200]
```
## Install
[](https://npmjs.org/package/tonal-freq/)
## API Documentation
* [freq](#module_freq)
* [`.eqTempFreq(ref, maxDecimals, note)`](#module_freq.eqTempFreq) ⇒ Number
* [`.toFreq(note)`](#module_freq.toFreq) ⇒ Float
* [`.eqTempFreqToMidi(tuning, freq)`](#module_freq.eqTempFreqToMidi) ⇒ Number
* [`.toMidi(freq)`](#module_freq.toMidi) ⇒ Number
* [`.note(freq, useSharps)`](#module_freq.note) ⇒ String
* [`.cents(base, freq)`](#module_freq.cents) ⇒ Integer
## `freq.eqTempFreq(ref, maxDecimals, note)` ⇒ Number
Return the equal tempered frequency of a note.
This function can be partially applied if note parameter is not present.
**Kind**: static method of [freq](#module_freq)
**Returns**: Number - the frequency
| Param | Type | Description |
| --- | --- | --- |
| ref | Float | the tuning reference |
| maxDecimals | Integer | (Optional) the maximum number of decimals (all by default) |
| note | String \| Pitch | the note to get the frequency from |
**Example**
```js
eqTempFreq(444, 4, 'C3')
const toFreq = eqTempFreq(444, 2)
toFreq('A3') // => 222
```
## `freq.toFreq(note)` ⇒ Float
Get the frequency of note with 2 decimals precission using A4 440Hz tuning
This is an alias for: `eqTempFreq(440, 2, )`
**Kind**: static method of [freq](#module_freq)
**Returns**: Float - the frequency in herzs
| Param | Type | Description |
| --- | --- | --- |
| note | Number \| String | the note name or midi number |
**Example**
```js
freq.toFreq('A4') // => 440
freq.toFreq('C4') // => 261.63
```
## `freq.eqTempFreqToMidi(tuning, freq)` ⇒ Number
Get the midi note from a frequency in equal temperament scale. You can
specify the number of decimals of the midi number.
**Kind**: static method of [freq](#module_freq)
**Returns**: Number - the midi number
| Param | Type | Description |
| --- | --- | --- |
| tuning | Float | (Optional) the reference A4 tuning (440Hz by default) |
| freq | Number | the frequency |
## `freq.toMidi(freq)` ⇒ Number
Get midi number from frequency with two decimals of precission.
This is an alisas for: `eqTempFreqToMidi(440, 2, )`
**Kind**: static method of [freq](#module_freq)
**Returns**: Number - midi number
| Param | Type |
| --- | --- |
| freq | Float |
**Example**
```js
freq.toMidi(361) // => 59.96
```
## `freq.note(freq, useSharps)` ⇒ String
Get note name from frequency using an equal temperament scale with 440Hz
as reference
**Kind**: static method of [freq](#module_freq)
**Returns**: String - note name
| Param | Type | Description |
| --- | --- | --- |
| freq | Float | |
| useSharps | Boolean | (Optional) set to true to use sharps instead of flats |
**Example**
```js
freq.note(440) // => 'A4'
```
## `freq.cents(base, freq)` ⇒ Integer
Get difference in cents between two frequencies. The frequencies can be
expressed with hertzs or midi numbers or note names
**Kind**: static method of [freq](#module_freq)
**Returns**: Integer - The difference in cents
| Param | Type |
| --- | --- |
| base | Float \| Integer \| String |
| freq | Float \| Integer \| String |
**Example**
```js
import { cents } from 'tonal-freq'
cents('C4', 261) // => -4
```