---
title: "Special Sound"
id: 63147
type: "computer_media"
slug: "special-sound"
url: "http://localhost/computer_media/special-sound/"
markdown_url: "http://localhost/computer_media/special-sound.md"
published_at: "2026-01-30T17:36:44+00:00"
modified_at: "2026-03-30T21:45:27+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2019/02/20230809-041332.jpg"
excerpt: "A tight three-voice AY chip sweep that drives harmonically spaced pitches across all tone channels before silencing itself and looping forever."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 2068"
    slug: "ts2068"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts2068/"
model:
  - name: "Timex/Sinclair 2068"
    slug: "ts-2068"
    taxonomy: "model"
    url: "http://localhost/model/ts-2068/"
indiv:
  - name: "Eric Boisvert"
    slug: "boisvert-eric"
    taxonomy: "indiv"
    url: "http://localhost/indiv/boisvert-eric/"
genre:
  - name: "Sound"
    slug: "sound"
    taxonomy: "genre"
    url: "http://localhost/type/sound/"
media_contents:
  - id: 63045
    title: "Byte Power September 1986"
    type: "computer_media"
    url: "http://localhost/computer_media/byte-power-september-1986/"
media_type: "Program"
programmers:
  - name: "Eric Boisvert"
    slug: "boisvert-eric"
    taxonomy: "indiv"
    url: "http://localhost/indiv/boisvert-eric/"
mediadate: "1986"
producer_company:
  - id: 25181
    title: "Byte Power"
    type: "company"
    url: "http://localhost/company/byte-power/"
article_media:
  - id: 63031
    title: "Better Programming"
    type: "article"
    url: "http://localhost/article/better-programming-4/"
media_type_tags: "Sound"
---

# Special Sound

Special Sound is a short music/sound demonstration that sweeps three simultaneous tone channels of the TS2068’s AY-3-8912 sound chip through a rising frequency sequence. A FOR loop drives register pairs so that three voices play harmonically offset pitches (x, x+8, and x+12) while shared amplitude registers are held at maximum volume (15). After the sweep completes, a brief shutdown sequence silences all channels and an envelope register is set before the program waits for a keypress and loops indefinitely.

***

## Program Structure

The program consists of just four logical sections compressed into three executable lines:

1. `REM` header (line 0) — title and copyright notice, no executable content.
2. Line 10: initialises `y=0` and opens a `FOR` loop, `x=0 TO 140`.
3. Line 20: issues a single multi-register `SOUND` statement per iteration, then `NEXT x` closes the loop.
4. Line 30: shutdown `SOUND` call, `PAUSE 0` to wait for a keypress, then `GO TO 1` — which targets the non-existent line 1, so execution falls through to line 10, effectively restarting the sweep.

## AY-3-8912 Register Usage

The TS2068 exposes the AY sound chip through the `}` (`SOUND`) keyword. Each `SOUND` call accepts register/value pairs. The registers used here are:

| Register | Function | Value in loop |
| --- | --- | --- |
| 0 | Channel A fine pitch | `x` (0–140) |
| 1 | Channel A coarse pitch | `y` (0) |
| 2 | Channel B fine pitch | `x+8` |
| 3 | Channel B coarse pitch | `y` (0) |
| 4 | Channel C fine pitch | `x+12` |
| 5 | Channel C coarse pitch | `y` (0) |
| 7 | Mixer (tone/noise enable) | 56 (all tones on, noise off) |
| 8 | Channel A amplitude | 15 (maximum, no envelope) |
| 9 | Channel B amplitude | 15 |
| 10 | Channel C amplitude | 15 |

Mixer value 56 in binary is `00111000`, which disables noise on all three channels while enabling tone output — a standard configuration for pure-tone music.

## Notable Techniques

- **Harmonic offsets:** The three voices are pitched at `x`, `x+8`, and `x+12` respectively. Because AY pitch registers are inversely proportional to frequency, fixed additive offsets produce a consistent (though not perfectly equal-tempered) harmonic spread across the sweep.
- **Single SOUND call per frame:** Grouping all ten register writes into one statement minimises interpreter overhead inside the loop, keeping the sweep reasonably smooth.
- **Shutdown sequence (line 30):**`SOUND 10,16;8,16;9,16;12,20;13,0` sets channel amplitudes to 16 (envelope-driven mode), programs the envelope period (register 12), and resets the envelope shape (register 13 = 0), providing a tidy release rather than an abrupt cutoff.
- **Restart via GO TO 1:**`GO TO 1` with no line 1 defined causes the interpreter to find the next available line (line 10), making this a concise infinite-loop idiom without needing `GO TO 10`.
- **Variable `y=0` as coarse pitch:** Holding all coarse pitch registers at zero limits each voice to the lower 8-bit range of pitch values, keeping frequencies in the audible mid-to-high range during the sweep.

## Source Code

```
   0 REM                                                            Special Sound                   Written by Eric Boisvert        ©1986 BYTE POWER                 
   10 LET y=0: FOR x=0 TO 140
   20 SOUND 0,x;1,y;2,x+8;3,y;4,x+12;5,y;8,15;10,15;9,15;7,56
   30 NEXT x: SOUND 10,16;8,16;9,16;12,20;13,0: PAUSE 0: GO TO 1
```