- First two channels: Pulse wave with three different duty cycles
- Third channel: Fixed-volume triangle channel
- Fourth channel: Noise channel (can work in both pseudo-random and periodic modes)
- Fifth channel: (D)PCM sample channel
Effects
| Effect | Description |
|---|---|
11xx | Write to delta modulation counter Range: 00-7FThis may be used to attenuate the triangle and noise channels (see “non-linear mixing” below) Will not work if a sample is playing |
12xx | Set duty cycle or noise mode Pulse channels ( 0-3):• 0: 12.5%• 1: 25%• 2: 50%• 3: 75%Noise channel ( 0-1):• 0: Long (15-bit LFSR, 32767-step)• 1: Short (9-bit LFSR, 93-step) |
13xy | Setup sweep upx: Timey: ShiftSet to 0 to disable |
14xy | Setup sweep downx: Timey: ShiftSet to 0 to disable |
15xx | Set envelope mode (pulse and noise channels only)0: Envelope + length counter (volume = envelope duration)1: Length counter (volume = output volume)2: Looping envelope (volume = envelope duration)3: Constant volume (default, volume = output volume)You may need to apply a phase reset to make the envelope effective |
16xx | Set length counter See table below for possible values This will trigger phase reset |
17xx | Set frame counter mode0: 4-step (NTSC: 120Hz sweeps/lengths, 240Hz envelope)1: 5-step (NTSC: 96Hz sweeps/lengths, 192Hz envelope) |
18xx | Set PCM channel mode00: PCM (software)01: DPCM (hardware)In DPCM mode, samples will sound muffled and available pitches are limited |
19xx | Set triangle linear counter00-7F: Set the counter80+: Halt it |
20xx | Set DPCM frequency (DPCM mode only) See table below for possible values |
Non-Linear Mixing
The triangle, noise, and PCM channels are mixed together non-linearly such that the level of the DMC (the “delta modulation counter”, representing the PCM channel’s amplitude) inversely affects the volume of the others. This can be intentionally used with effect11xx to hold the DMC at a level that lowers the volume of the triangle channel in a controlled fashion; at maximum DMC level (117F) the triangle plays at about 57% of full volume.
DPCM Samples
Due to hardware limitations:- A loop in a DPCM sample must start on a multiple of 512 samples (512, 1024, 1536…)
- Loop length must be a multiple of 128 plus 8 samples (136, 264, 392…)
Envelope Mode
Both pulse channels and the noise channel have a simple hardware envelope generator with two modes:- One that holds the volume at whatever the software sets
- One that creates a downward ramp of volume starting from maximum and counting down to 0
Frame Counter
The frame counter is a global counter that controls the speed of hardware envelopes and sweeps. The resulting speed depends on both the chip’s clock rate and whether it’s set to 4-step or 5-step mode.Length Counter
Setting the length counter will automatically stop a note after the specified amount of time. See the length counter table below for effect values and their corresponding durations.Chip Configuration
The following options are available in the Chip Manager window:- Clock rate: Sets the rate at which the chip will run
- DPCM channel mode: Allows you to set which mode to use for the DPCM channel
- DPCM: The default mode, playing 1-bit DPCM samples as supported by the hardware
- PCM: This mode provides crisper 7-bit samples by writing to the delta counter directly. Uses a lot of CPU time in console