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### The H command

An **H** included in any string immediately turns off the **PLAY** command. The main use of this is where you have an infinitely repeated bass line in one string. You can stop this at the end of the tune by putting an **H** on the end of the string which plays the melody.

### Comments

You can include reminders and comments anywhere you like by using **!!** marks. Anything written after a **!** will be ignored until the next **!** or the **"** at the end of the string is reached, for example:

```
10 PLAY "abCDEFG!chorus!aCEaDG"
```

### Channel selection

The command **M** is used to select which of the three *channels* are in operation per *PSG* and whether these give *noise* or *musical tones*.

You can have a maximum of *nine channels* (*three* per *PSG*) in use at any one time, but it does not matter whether they are all *tone*, all *noise*, or a mixture of both.

Your choice is entered with a number following the **M**, worked out like this:

<table>
<thead>
<tr><th></th><th colspan="3">Tone Channels</th><th colspan="3">Noise Channels</th></tr>
</thead>
<tbody>
<tr><th>Channel</th><td>A</td><td>B</td><td>C</td><td>A</td><td>B</td><td>C</td></tr>
<tr><th>Number</th><td>1</td><td>2</td><td>4</td><td>8</td><td>16</td><td>32</td></tr>
</tbody>
</table>

*Table 13 – Channel audio type selection codes*

Mark each *channel* you want to turn on, and note down its number from the table above. Then just add them together to get the code you should use after the **M**. For example, if you want to use *tone channels* **A**, **B**, and **C**, you add the numbers **1+2 +4 = 7**, so you use the command **M7**. In the same way, **M56** would turn on *noise channels* **A**, **B**, and **C**.

*Noise* can be used on any *channel* but the most wide-ranging frequencies are available in *channel* **A** for each *PSG*. For the best results, put your sound effects in the string which controls this channel for each *PSG* – *1<sup>st</sup>*, 4<sup>th</sup> and 7<sup>th</sup> string, in other words the first string per *PSG* after the **PLAY** command.

### Stereo control

The **PLAY** commands **L**, **R** and **S** control the stereo image for each *PSG*. The first two restrict the current *PSG*'s audio output to *Left* and *Right* speakers respectively while the latter resets the Stereo image. If your ZX Spectrum Next is set up with **ABC stereo** (the default), normally *channel* **A** goes to the left speaker, **B** goes to left and right, and **C** goes to right.

Therefore, if the **L** command is used, only *channels* **A** and **B** from the current *PSG* will be audible. Similarly, if **R** is used, only *channels* **B** and **C** will be audible. Like the **M** command, the **L**, **R** and **S** commands need to be re-entered in the strings targeting each *PSG*.

### Digital Audio

Your ZX Spectrum Next also contains hardware that can output digital audio, that is sound previously recorded digitally for reproduction, in a similar manner to your house or car CD and MP3 players. There is no easy way to manipulate this hardware from *NextBASIC* so *NextZXOS* provides several *dot commands*[^p153-1] (more on *dot commands* in *Chapter 19 –*

[^p153-1]: Dot commands are short programs residing in folder **c:/dot/** which are used to extend **NextZXOS**, or to expose facilities not normally available to NextBASIC to the user. Dot commands were originally created for **esxDOS** (an alternative, free, ZX Spectrum–compatible Operating System which also works on the ZX Spectrum Next) and whose format was adopted by **NextZXOS** via its **esxDOS** emulation layer. Most **esxDOS** dot commands will work with **NextZXOS** and vice-versa unless they use some special facility not covered by either the **esxDOS** emulation layer or they are OS or machine dependent.