Covox Music Device Review on Spectrum

Not long ago, the topic of Covox was raised once again among spectrumists. As an “old spectrumist”, I formally understand what this is about, but I have never had a hardware device. It did not take root at points of sale in my city, and at that time there was no necessary understanding and knowledge for independent interest. The search for information yielded a significant number of different schemes and other technical things, but to my great surprise, there was no description for the average person of “what it is and how to eat it”. I think it is worth filling this gap.

The article was published in 2021 in Issue 29 of the ZX Spectrum magazine “ZaRulem Printed Word”.

The article was co-authored with Vadim Chertkov.

The following definition can be found on the Internet:

Covox — the simplest device for playing digital sound. It is an 8-bit resistive DAC (R-2R circuit) connected to a parallel port. Under this name, it was initially released in 1986 by Covox for IBM PC-compatible computers. Subsequently, this name began to be applied to all similar devices. Around the same time, similar devices from other manufacturers appeared, and the device began to be used on various platforms, including the ZX Spectrum.

In other words, Covox can be called the world's first sound cardIts advantages include:

• Simplicity of the circuit and low price of the finished device.

• Good quality 8-bit sound. Technical characteristics of which depend on the capabilities of the computer and software package. Theoretically, you can get sound at the level of the Sound Blaster 1.0 music card.

• Easy to connect to a computer. Usually connected to an LPT port, but there may be other options.

• Ease of programming.

The disadvantages include the fact that Covox itself is only plays soundwhich requires a significant load on the central processor and an incomparably large consumption of RAM compared to AY.

But the Spectrum has a music coprocessor AY, so what is the benefit for us?

To fully answer this question, you need to understand what the difference is between AY and Covox.

The AY music coprocessor is three-channel sound generator. It is more correct to call it a synthesizer with additional capabilities for sound synthesis, so that the music is more interesting. That is, the main program only gives the AY command that it needs to play such a note with such characteristics and in such a mode, the music coprocessor does everything else itself. It is with such a scheme that the central processor is loaded insignificantly, which allows using AY in a wide range of tasks.

Covox only plays digital audio (Samples), which was previously obtained using analog-to-digital converter (ADC). Digitized instruments (Samples) are a file consisting of a set of instantaneous amplitude values ​​in each signal sampling period. The shorter the period between samples, the higher the instrument digitization frequency, which means that the sound quality of the digitized instrument will be closer to the real one.

The AY music coprocessor is also capable of playing digital audio, but only at 4-bit resolution, while Covox plays full 8-bit audio. Music played on Covox will sound closer to the original.

What is better: sound generation or digital sound reproduction (Samples)?

Ultimately, much will depend on the skill and talent of the author of the melody. But the synthesis of notes by the AY music coprocessor is limited by its technical characteristics, although it allows you to perform various additional effects on them without requiring additional processor time.

Whereas Covox will reproduce absolutely any sound that has been previously digitized. This allows for the reproduction of voice and other complex sound effects.

In my personal opinion, all other things being equal, the quality of the melodies on Covox is higher. But this comes at the cost of a significant load on the central processor and the consumption of RAM.

I believe that Covox is one of the most underrated devices on the Spectrum, the use of which would raise the sound design of programs to a completely new level. On the one hand, this can be explained by the above-mentioned shortcomings of Covox: significant load on the central processor and high consumption of RAM. On the other hand, memory over 128 KB began to appear on Spectrum clones since the first half of the 90s – here is the place for up to 1 MB for high-quality sound. The problem of high load on the central processor can be solved by using the “turbo mode”, which is available on most domestic clones. And also by organizational measures – high-quality sounds can be used to voice those places when there is no other large consumption of processor time in the game, for example, “fatality” or the death of the main character, the selection of objects in games like “Dizzy”, etc. At the same time, if the Covox device is not installed on the computer, these same effects can be output to AY, albeit in worse quality. The combined use of AY and Covox can open up completely new horizons. For example: music that uses both devices will not only combine the advantages of both, but will increase the total number of independent voices.

There are a lot of Covox circuits. Both the simplest ones, on 18 resistors, and those using specialized digital-to-analog conversion (DAC) chips. In the USSR and Russia, the 572PA1 chip (analogous to AD7520) is most often used in this role. It should be noted that devices assembled according to circuits on 18 resistors have an unpleasant effect in the form of a large amount of extraneous noise when playing sound. Although even in this form, the sound will be much better than on AY. When using the 572PA1 chip or similar, the sound will be even better, but in this case it will not be possible to completely get rid of extraneous noise, although you can hear it only in headphones. There is a backwards compatible Soundrive device, which is a four-channel version of Covox, in which it was possible to completely get rid of all noise. But it is already much more complex, and therefore more expensive.

On different machines, when using different Covox device connection schemes, different ports are used for sound output. Usually, for Pentagon, port #FB is used, and for Scorpion, port #DD is used. On Profi, stereocovox is connected to ports #3F and #5F. On other clones, there may be other ports. But the general sound output scheme does not change from this. Therefore, when using Covox, you need to specify the output port in the program settings.

Currently, there are already a significant number of music cards with great capabilities for the Spectrum. But they all require a unique code for their support. However, most of them are capable of working in the Covox device imitation mode. Due to this, you can use Covox as a unifying element and implement support for all music cards at once on its basis by writing a universal code for outputting music and sound effects.

Software support for Covox on Spectrum is unfortunately not very large. There are a couple dozen demos for TR-DOS, several games were voiced for Covox, there are several music players of different formats, a digital music editor and a digital sound editor. Most of the programs can be found on the “Virtual TR-DOS” website (https://vtrd.in/). There are also programs for CP/M OS.

Since I am a Profi computer user, I am most interested in the Covox version created for it. Let's get to know it in more detail.

This version is commonly called Profi Covox. Its key feature is that it is a stereo device, i.e. it has two physical sound channels. Despite the fact that this version of Covox was developed for a competitive computer, it can be easily installed on any Spectrum clone. We will look into programming Profi Covox in one of the following articles. In the meantime, let's get acquainted with general questions. Here is the Profi Covox diagram.

There are two WAV file players in the CP/M OS software. The first of them, distributed by Condor, can play a file of a maximum size of 51 KB. The second of them, authored by Vadim Chertkov, works in PQ-DOS OS and can play a file limited only by the size of RAM. There is also the ADJ music system (authored by A.A. Krestyanikov) for playing music files of the same format and the Synth-Master music editor (authors by Dmitry Volvach and Dmitry Tishchenko) allowing you to edit and listen to music in the ADJ and STM formats. The Synth-Master music editor is fully compatible with similar STM music editors on Amiga and IBM PC computers, which allows you to freely transfer music from these platforms. In the ADJ music system, you can also play music from other platforms, but after converting it to the ADJ format using a special utility.

Currently, there are versions of the programs “ADJ” and “Synth-Master” adapted for the General Sound music card.

Here are the characteristics of the programs:

As you can see, the music editor “Synth-Master” has slightly better characteristics. Which once again confirms the thesis that the sound quality of Covox depends not only on the hardware capabilities of the computer, but also on the software algorithms used.

Both programs come with good documentation, so for now we will limit ourselves to describing the minimum sequence of actions required to start playing a melody.

The ADJ music system uses the resident library of the Windows window interface in its work and it must be pre-loaded. So to run the program it is better to use the files adj.bat or adj-gs.bat to load the version for Profi Covox or for the General Sound music card, respectively.

The music editor “Synth-Master” uses an internal window interface, you don't need to download anything for it. But there are two versions of the program “Synth-Master” – regular and FAST (fast). The regular version (syntmast.com) supports downloading music files limited only by the amount of RAM. Whereas in the FAST version (smfast.com) the size of the downloaded file is limited to 128 kb for instruments, but the sound quality is much higher. For both versions there is an adaptation for the General Sound music card (sm-gs.com and smf-gs.com respectively).

After loading the program, you need to adjust it to the speed of your computer (emulator). In ADJ, you need to use the Options\AutoDefinition menu item, and in Synth-Master, the System\Auto Definition menu item. For the ADJ music system, this operation strictly requiredotherwise the quality of music playback will suffer greatly. For the music editor “Synth-Master” this action is optional, since in most cases it itself makes the correct adjustment to the computer speed. But it must be done if the “Turbo” button was pressed after the program was launched.

Music editor “Synth-Master”Next, if necessary, through the menu item “File\Drive…” select the drive in which the disk with music is located, and actually load the music. To do this, in the music system “ADJ” select the menu “File\Load…”, and in the music editor “Synth-Master” select the menu item “File\Read STM” or “File\Read ADJ”.

To start playback from the beginning of the melody, you need to select the menu item “Play\Begin”.

To interrupt playback in both programs, you need to press the “Space” key. To exit to the previous menu level, if you have an IBM keyboard: you need to press the “Esc” key, and if you have a standard Spectrum keyboard, then the key combination “Shift+1”.

We have the source code of the ADJ music system (author A.A. Krest'yanikov). Unfortunately, we do not have the source code of the Synth-Master music editor (authors Dmitry Volvach and Dmitry Tishchenko). The program manual states that the authors live in Zaporozhye, Ukraine, and provides contact phone numbers: Dmitry Tishchenko (0612) 63-40-63, Dmitry Volvach tel. (0612) 68-04-82. Unfortunately, we were unable to contact them using this information. Searching for contacts in other places also did not yield any positive results. So we would like to ask the readers of the magazine, if anyone has any information about the authors of the program or the ability to contact them, to share it or ask the authors to contact us, directly or through the editorial office of the magazine.

Now let's say a few words about emulators. Profi Covox support is available in the emulator “ZXMAK2” and in “UnrealSpeccy”, unfortunately, only in version “0.37.1m0 30 XT keyboard controller jan 2009 molodcov_alex”. The disadvantages of the emulator “ZXMAK2” include the lack of turbo mode, which affects the quality of playing melodies. And the disadvantages of the emulator “UnrealSpeccy” version 0.37 include the lack of support for disk images in the “PRO” format, which is insignificant in this case. So in the appendix to the article you will find a link to the archive of the emulator “UnrealSpeccy” version 0.37 configured to work in the Profi computer mode. In the disk drive “A:” there will be a disk image with the “ADJ” music system, in the disk drive “B:” a disk image with the “Synth-Master” music editor.

Articles, graphics – all this is very good and useful. But in the modern world there is another way to transmit information, which we have so far bypassed – I am talking about video clips. Despite the fact that this method has a number of disadvantages, it also has a certain set of advantages. Therefore, it was a pleasant decision to try myself in this direction. For which the YouTube channel “Through the Looking Glass” was created.

A computer geek, not quite an ordinary person. His life consists of two parts, and the dividing line runs along the glass of the monitor. One part is in the real world, and the second in an amazing country – Through the Looking Glass. And it is difficult to say which of the parts is more important. The channel is dedicated to all aspects of life on the other side of the monitor, in Through the Looking Glass. First of all, it will reflect those aspects of this world that are interesting to us, these are: ZX Spectrum, and OS / 2, and various programming languages, and much more. But the world of Through the Looking Glass is much more multifaceted, so if someone suddenly has a desire to reflect the side that is interesting to him, we will be happy to provide this platform. It is difficult to hope for frequent video releases, but they will definitely be – that's for sure.

The first videos on the Zazerkalye channel are examples of music playback on the Profi Covox device. This is a video clip for the song “Accountant” by the Kombinatsiya group and a video clip for music based on the film “17 Moments of Spring”. The videos are accompanied by frames in the format of an extended Profi computer screen with a palette of 16 out of 256 colors.

Well, that's probably all for now. If you have any questions, you can ask them at the following addresses:

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