In this section, we tend to encounter a Programmable Sound Generator (PSG), a sequencer or a large mixer. This is because, at the end of the day, dedicated audio hardware is meant to offload audio operations from the CPU. Although if this hardware turns out to be 'weak', it degrades the sound capabilities of the console.
Now, what we consider 'sound hardware' in the PSP is very bare-bones: only two PCM channels and a stereo mixer. The maximum sampling rate and resolution are 48 kHz and 16-bit, respectively.
I don't see any of the accelerators I mentioned in the first paragraph. So, does this imply that the sound will be as limited as other cases showed? No! Because the PSP relies on software to compensate for this.
You see, while there isn't a large amount of sound-related circuitry, Sony supplied a lot of general-purpose components. These can help with audio decoding, streaming and mixing. I'm talking about the Media Engine.
That block is very good at signal processing, but it needs to be programmed. So, Sony wrote the following software for the Media Engine to complement the two PCM channels (we'll call these the 'endpoint') :
- Sound driver: talks to the endpoint and performs memory transfers using DMA.
- Software audio synthesizer: as the name indicates, it generates the signals to be sent to the endpoint.
- This synthesizer supports 32 channels, using the PCM, ADPCM or ATRAC3 formats .
- Provides digital reverb, pitch control and ADSR envelope.
Games don't have access to these modules directly. Instead, they call many libraries included in the official Software Development Kit (SDK). Some libraries are designed to operate raw signals while others are optimised for particular applications. Examples include:
- MP3 and AAC decoding.
- MIDI sequencing.
- Voice over IP (VoIP) audio decoding (G729 and u-law).
- The operating system of the PSP bundled a variant of the 'Skype' app, if you wonder what uses VoIP could have here.
Audio comparison
Let's put all this into practice by taking a look at how games reproduced their sound. I wrote this special player that allows you to swap between consoles (to enable side-by-side comparisons):
Nintendo DS:
Click to listen
PSP:
Click to listen
Interactive player available in the modern edition
Audio samples
Nintendo DS: Final Fantasy IV (2007).
PSP: Final Fantasy IV - The Complete Collection (2011).
PlayStation 2:
Click to listen
PSP:
Click to listen
Interactive player available in the modern edition
Audio samples
PlayStation 2: Kingdom Hearts 2 (2005).
PSP: Kingdom Hearts Birth by Sleep (2010).
In the first example, the Nintendo DS game sequences its music on the fly, while the PSP one decodes ATRAC3. As you can hear, having no dedicated sound hardware per se doesn't imply poor sound quality. In fact, one could argue the opposite, as the Media Engine provided more features than the sound chips of most previous portable consoles ever did.
The second example is much trickier to quantify. I placed a PS2 tune for comparison, but I had to boost the PS2 one a bit (I presume PSP soundtracks are louder to compensate for the smaller speaker and the proximity to the user). Also, bear in mind that the arrangements are slightly different between platforms. It's possibly just a creative change since the PSP game was released five years after the PS2 one. Overall, the PSP doesn't show deterioration (considering that the PS2's SPU2 is very powerful and flexible).