Just like its graphical abilities, the audio department of this console has undergone a significant overhaul. I would argue it even offers the most advanced synthesising techniques of its generation.
Architecture
Some companies partnered with Yamaha, while others devised an in-house solution. Well, Nintendo partnered with Sony - the electronics conglomerate behind the Walkman - to supply a sophisticated synthesiser.
And so, Sony delivered quite an audio subsystem, consisting of the following components:
- The S-DSP: Plays ADPCM samples across eight channels, they are mixed and sent through the audio output. The S-DSP processes samples with 16-bit resolution at a 32 kHz sampling rate, and offers various sound manipulation techniques:
- Stereo Panning: Distributes audio channels to create a stereo soundscape.
- ADSR Envelope Control: Adjusts how the volume changes over time.
- Delay: Simulates echo effects. It also includes a frequency filter to cut out selected frequencies during the feedback (not to be confused with Reverb!).
- Noise generator: Generates pseudo-random waveforms resembling white static.
- Pitch modulation: Allows some channels to influence each other's pitch, similar to FM synthesis (used by its competitor).
- The SPC700 CPU (also known as 'S-SMP'): An independent 8-bit CPU that drives the S-DSP and receives commands from the main CPU .
- 64 KB of PSRAM: Stores audio data and programs, with the main CPU responsible for loading content into it.
- If 'Delay' is enabled, some memory is reserved for feedback data. This can be dangerous - if not managed carefully, feedback storage could override existing data!
The audio subsystem operates in parallel with the main CPU. When the console powers on, the SPC700 boots a 64-byte internal ROM that sets it up to receive commands from the main CPU . After this setup, it remains idle until instructed.
(Video) Channels used for melody.
(Video) Drums are discriminated for demonstration purposes.
(Video) All audio channels.
For the S-SMP to do independent work, it needs to load a type of program known as Sound Driver. This software instructs the chip on how to manipulate raw audio data sent by the main CPU to PSRAM, as well as how to control the S-DSP.
Considering the overall capabilities of this system, most games bundled sound drivers that performed music sequencing. Similar to MIDI, they drive the S-SMP and S-DSP to read sampled instrument data and subsequently play it at different pitches and effects to produce the musical score. This was something that this console excelled at.
As evident, the sound subsystem represented a major leap forward compared to previous generations, but it also posed significant programming challenges. Nintendo only provided one driver, the Nintendo SPC Sound Engine . Along with it, the documentation was infamous for its vague explanations and omission of critical features.
All in all, this forced developers to conduct their own research and derive their own implementations if they wanted extra functionality. Consequently, a wide variety of sound drivers emerged in the market , with some uncovering impressive capabilities.
Pitch control
Pitch bending enables to produce distinct notes using the same sample. Well, the S-SMP included a useful bender to alter the pitch in a smooth manner. Take a look at this extracted channel from Mother 2/Earthbound, both examples come from the original soundtrack, however, the first one has the pitch control disabled.
Video - No pitch bend.
Video - With pitch bend enabled.
Evolution from the NES
To visualise the evolution of sound from the NES to the Super Nintendo, here is an excerpt from two music scores - one from an NES game and another from its Super Nintendo sequel. Both feature the same composition.
Video - Mother (1989).
Video - Mother 2/Earthbound (1994).
Advanced usage
(Video) Channels used for melody.
(Video) Channels used for drums.
(Video) All audio channels.
Here's a more instrument-rich composition that takes great advantage of pitch bending, echo and envelope.
This combination of techniques allowed the music to only require five channels in total, leaving the other three for sound effects.
Stereo confusion
The S-DSP's volume controls are organised into signed 8-bits values , meaning that volume levels can be set to negative values. But hang on, if '0' represents mute, what happens when the volume is set to '-1'? Well, it inverts the signal.
This technique is particularly useful for creating a surround effect, accomplished by setting the stereo channels out of phase - where one channel outputs the normal signal while the other outputs the same signal but inverted.
Unfortunately, abusing this feature results in very unpleasant results, such as the feeling that the music is playing inside your head. For this reason, most SNES emulators bypass this setting altogether.
Additionally, out-of-phase stereo is cancelled out on mono devices, so those games needed to provide a stereo/mono selector to avoid muting their own soundtrack.