• Atari ST SDH files
• MP3 files
• High definition wav files

and many, many more.

The way the system works is as follows: The ZX Spectrum Next communicates with the Accelerator via its secondary UART² and sends commands and audio files to the specialised SUPervisor software that is running on the Raspberry Pi Zero. The Pi Zero in turn interprets these files and reproduces the audio contained therein via it's GPIO port onto the ZX Spectrum Next I²S³ port which in turn mixes it with the rest of its audio output and redirects it to whichever output you have available. In essence when it comes to playback, the ZX Spectrum Next is considered a "sound card" where the accelerator is concerned and two extra DACs where the ZX Spectrum is concerned. As a consequence you can have Digital Audio (on the ZX Spectrum Next), all three PSGs playing AND Digital Audio (on the Pi Zero) all playing simultaneously!

To use the Pi audio facilities you need to first enable the secondary UART and set it to the accelerator. In NextBASIC or the Command Line you must type:

CD "c:/apps/rpi"

and press ENTER. Then type:

LOAD "pi.bas"

You'll get a message stating 9 STOP statement, 50:1indicating the system is now ready to play audio using the Pi Zero. Feel free to poke about the listing of the PI.BAS program as it shows you the usage of Next Registers (see Chapter 22 for more).

Playing audio files requires a dot command called .pisend which you can find in c:/dot/ which serves a two-fold purpose: to send files to the Pi Zero's temporary storage and send the appropriate command for it to play. Thankfully D. Rimron-Soutter and David Saphier, maintainers of NextPi2⁴ and .pisend respectively, have packaged all this nicely into little NextBASIC programs (located in c:/nextzxos/) which you can either call directly or via the Browser by selecting a filetype already registered. Currently registered filetypes include .SID, .MOD, .XM, .TZX and .SDH.

To illustrate how this works, we shall attempt to play an Atari™ SDH file. Assuming you have a SDH file named warhawk.sdh (search for it and download it on the internet; it's freely available) on the root of your SD card, playing it is as simple as:

LOAD "c:/nextzxos/sndplay.bas":
 f$="c:/warhawk.sdh":GO TO 10

The screen will read Playing... c:/warhawk.shd and the music will start playing from your speakers.

External Audio Output

If you are interested in doing more with sound from the ZX Spectrum Next, like hearing the sound that BEEP and PLAY make on something other than the usually limited audio of your display, you will find that the audio signal is also present on the Audio Out socket on the back of the machine. You may use this to connect to a pair of headphones or a higher quality amplifier. Note that this will not disrupt audio reproduction on the digital display ca-

² UART or Universal Asynchronous Receiver-Transmitter is a hardware device that exchanges data sequentially between two systems. In our case this is done between the ZX Spectrum Next hardware and the Pi Zero accelerator via its GPIO port. ³: I²S or Inter-IC Sound is a serial bus interface standard to connect digital audio devices. ⁴: NextPi/2 is the operating system running on the Pi Zero accelerator that's purposely built to support the Next.