Silly Sound Bastard: yet another Covox Speech Thing clone

hello and welcome for a project which i'm currently working on i needed to build some pcbs but my practice in electronic design automation or short eda was already many years ago so i wanted to refill this gap and tried some of the common eda tools out there but to get into it you need a good and simple project to start with and what is simple enough and still finding useful a coverage speech think loan if the name covox doesn't ring the bell for you then you probably missed one of the most important and funny gadgets for audio output which ever existed for a computer of the late 80s and early 90s the covex pitch thing was an external audio device attached to the computer to output digital sound it was very primitive composed of just couple of resistors and a mono-analog signal output usually it was plugged into the printer port of a ibm pc compatible but it was also widely used mode for other personal computers like zx spectrum a similar very famous device with some differences was the disney sound source however these two devices despite a very similar principle were unfortunately incompatible to each other as i was a child around 12 or 13 years old a real sound card was just not affordable for me and my friends so we made couple of covox clones with the parts we could find around unfortunately i can't provide original pictures anymore but they were ugly diys and with worst audio quality you can imagine and still they were superior to what the normal pc speaker could deliver by far now many years later i decided to rebuild a kovx clone again and use it as a simple example to regain some practice in eda and hopefully this time it is going to be a little bit better than back in the days without going into details too deep how does kovacs speech thing work well as i already told it is mainly just a simple digital to analog converter built of handful of resistors a parallel port on the pc is capable to output 8-bit data simultaneously on its pins 2 through 9. so if some generated digital sound would be sent to the parallel port in 8-bit samples it would be possible to output the sound unfortunately common speakers do not understand digital signals instead they need some analog signal in form of changing voltage in some range so actually what we have to do is to convert the digital output which is coming from the parallel port into analog output to be able to connect a usual speaker an 8-bit sample can represent a discrete value between 0 and 255 where every bit again represents 5 volts with 1 and 0 volts with 0. so every bit must be mixed into a common analog signal where the final output voltage of all bits must be mapped between 0 volts and 5 volts this is done by a simple but clever arrangement of some resistors this schema is also called rtr dac and is very handy when a simple digital to analog conversion has to be done i will not explain in detail here how it works but there is a very nice document by evgeny brijkov about it with full of useful background information and mathematical explanation of the functionality i will put the link into the description and i highly recommend to take a look if you are interested in details if you search the internet you will find a lot of schematics for the cover speech thing most of them are more or less similar with only simple passive elements and without the need for external power supply however you can also find some more sophisticated solutions without any resistor based deck but using ics to convert stabilize and amplify the sound such variants have probably a lot better output quality but the parts are also more sophisticated and they need external power supply since the parallel port doesn't provide any power and since i wanted to keep it as simple as possible i decided to go with a simple solution without using any chips however i also wanted to have some space for experiments and so i added some elements which you usually don't see on another versions first of all to get a better audio quality you have to use good quality resistors with one percent variance here it gets a little bit tricky since you need to find resistors with two to one value relation and it has to be as exact as possible well since the resistance value of two resistors in row is a sum of their values and since the size of the board was not important for me i decided to increase the amount of resistors and could use therefore all resistors with the same value as for parallel port connector i decided to use etch mount and not a through hole connector since i have a lot of db25 connectors and printer cables and my spares so i could reuse them furthermore i added a couple of bypass capacitors to be able to play with low pass filtering and last but not least a deep switch array to control the capacitors as well as to turn fake stereo on or off as you probably understood already covers is mono only in its pure shape however if you connect a stereo speaker you probably would like the sound to come from both speakers why i made it switchable you may ask well first of all because i could and about the second interesting reason i will talk a little bit later for now i just say real stereo sound anyway i drew all the schematics and ordered the pcbs from china around a week later i got this package and i would like to present to you the silly sound bastard the pcb turned out pretty nice and i'm very happy with the result since i made everything with through-hole parts only this soldering was a child's play one important note is that the higher resistor values you choose the less noise will come through the parallel port but also the output level will be lower and you will need an amplifier i wanted to use it completely passive with my headphones so i have chosen the resistors with much lower value than the original cover speech thing instead of using seven and a half kilo ohm i built this bastard around one kilo ohm resistors leather i actually soldered two versions to compare one with 26 one kilo ohm resistors and one with nine two kilo ohm resistors plus eight one kilo ohm resistance i use resistors with one percent variance which should be okay and this is how it looks like unfortunately i ran out of capacitors between 100 nanofarads and one microfarad so i use only the two i had the last one is definitely too much but a nice option for experiments enough blah blah time to make some noise to test the sound bastard i will use a dedicated either parallel port it is just a normal lpt port like any other regarding the software there are plenty of music players which support coverage speech thing as output device however different software call it differently sometimes it is covax or speech thing or sometimes dac in lpt or simply deck in the end just different names for the same device i will play a track and switch between different settings turning the fake stereo output as well as different filtering options on and off [Music] do [Music] [Music] [Music] [Music] well that doesn't sound that bad for 8-bit music don't you think i have to admit that one microfarad filtering was too much however this filter didn't sound that dull when i was using it with my headphones there the 100 nanofarad filter didn't make any difference at all on the other hand first during recording both filters turned out to be that hard i guess it depends very much on speakers which filter is the best choice anyway that's why i made it switchable in the first place it is interesting to experiment with different filters and combinations but i guess nobody would want to go with more than one microfarad which is already without a question too aggressive okay nice we can play music in quite a good quality what's next the deck can only output in mono by connecting left and right channels we just fake stereo by just playing the same audio stream on both speakers however what about real stereo since i have a pair of these decks i can take a second parallel port expansion card and connect the second sound bastard there so one deck would be responsible for the left channel and the second for the right one i just have to mix the two mono outputs in one stereo signal and after months of hard engineering and fine tuning to suffice the high standards of the silly sound bastard i proudly present to you the mixer well actually these are just two mono jacks connected to the right and the left channel of one stereo jack please don't judge me on that one but it does what it should however there is one tiny problem with it i found only monojex in my spare box and this can end up in a problem a look at this schematics of a normal three and a half millimeter audio jacks it is divided in three sections d r and s which stands for tip ring and sleeve there is no standard but usually t is used for the right channel r is used for the left channel and s is common ground if you take a look at a mono jack it has only two sections t for the one channel and s for the ground a mindful viewer probably already understands what will happen if a mono jack will be plugged into a serie port the r and s will be shorted usually this would mean that one of the stereo channels would be grounded but the other channel would continue to work well yeah this could be a problem for the silly sound bastard since the fixed hero is just the same signal connected to the left and right channels of the audio jack and what will happen if one of the channels will be grounded exactly the other one will be grounded as well and we will get no sound at all luckily i made the fake stereo features switchable so we can disconnect the right and left channels from each other so the ring section on the jack will be just floating around and doesn't impact the tip when grounded okay let's now put both lpt port cards with deck in each one of them and try to make some stereo music some players do support stereo output onto lpt ports like the mode file editor or short fit which i'm using i've chosen one audio track which is especially good to test stereo sound this action [Music] that sounds really decent don't you think not bad at all for a bunch of resistors here is another track which you already heard in mono [Music] do [Music] okay that's really nice playing music in dos is great the silly sound bastard is a nice diy device you may think but what about the real thing what about gaming how useful can it be there well let's call it semi-useful if you want to use it as a replacement for a sound blaster compatible sound card first of all any cox clone is just a digital to analog converter and it can only output digital effects but can not handle fm sound like you would know it from edlib for example however as you already have heard it is still by far better than a plain pc speaker but if you search for a list of games which do support coverage speech thing directly you will be probably disappointed there are only less than 60 games and most of them are not well known however there is a tool named tmo which turns the emulation of 10d sound system on covox it also does kind of disney sound source emulation but it doesn't really work i'll come back to this later you can use the ammo with arguments l1 or l2 for lpt1 or lpt2 port accordingly and after that dendizon should work in many games let's try monkey island [Music] [Laughter] [Music] i call it a nice upgrade over a pc speaker another example which partially works is gods you just have to set up 10d sound output [Music] [Music] the intro music does work well however there are no in-game sound effects at all another good working example using the tandy emulation is eye of the beholder where not only the music but even sound effects do work without an issue [Music] but there are also examples which do not work out of the box prince of persia remains completely silent if you set up 10d sound option however as i already mentioned the ammo emulates also disney sound source and you can use it there for sound effects furthermore you can set up ps1 audio option for music which also seems to work then [Music] and here is a problem with a disney sound sword simulation as you probably noticed the effects are very distorted this is due to incompatibility between a covox and a disney sound source audio format as i mentioned earlier this new sound source accepts only 7khz sample rate where covox rate is variable and defaults at 11 kilohertz there are more differences between them but already this sample rate difference breaks most of the sounds here is another example which actually supports disney sound source wolfenstein 3d you can use it there for digital effects other effects and music is only supported with ad-lib compatibles despite of the unknown harm in the background you can probably hear how high-pitched the audio effects are this is how it sounds if you try to play 7khz samples at 11khz despite of that the sound effects are big deal over a pc speaker so using our silly sound bastard with the ammo we can play quite a lot of tandy sound compatible games definitely not all of them due to different reasons but quite a lot the list contains almost 450 games and many of them are very well known titles for example all the famous quests made by sierra but wait this is not yet the end of the possibilities there is another tool for covox which can emulate the sound blaster for digital effects i think i don't need to mention how long is the list of games which do have support for sound blaster you can call vsbe again with l1 or l2 for the lpt port and make some additional settings like irq if i now start wolfenstein 3d again you can see that soundblaster was detected again we can use only the emulation for digital effects but not for fm sound now you can hear that the sound effects are perfectly fine but the sound last emulation messes something up and the game runs extremely fast it is almost impossible to play it if i now start prince of persia again and set up sound blaster for digital effects we will not hear any music because tainty emulation is not off but we will hear clean sound effects like we know them from genuine sound lester [Applause] hmm interesting effect is that if i restart wolfenstein 3d again after i rent prince of persia i will get both sound source and sound blaster detected but more important is that the game now runs at normal speed with perfect digital audio effects the soundblaster emulation opens a huge list of potentially supported games however the fact that the emulation is a dirty hack and messes up on the low level with the machine degrades the expectations and to prove that there is indeed something evil happening look at the clock yeah well what's the conclusion such an audio device is really exciting not at least because it is so simple the audio quality it can output is though impressive even real stereo sound is possible if you use two of those i don't know any games which would be able to output stereo sound onto decks like i've shown it with a music tracker but still you can even play games on it to some extent maybe the question is if you need this it depends despite of the eda experience which i wanted to improve with it i found it very cool if you just want to play old classics you probably better get a sound blaster but if you are interested in computer history or you like to tinker with such things build your own devices for experiments then go for it hands down also if you have a machine without any expansion slots but with a parallel port like an old notebook for example this device can be interesting for you as well this project is open source and i will put the link into the description you are free to order the pcbs and solder your own silly sound bastards if you are interested there are two versions of it along which i've shown in this video and a short one and this is it from me i hope you enjoyed it i'm sorry for the best screen capture quality my camera just has problems to focus on the display and i'm working on a solution for a real screen capture in the future you can find the links to audio tracks which i use in this video in the description please don't forget to like or dislike and leave your comments below and so far thank you and goodbye [Music] do [Music] so [Music] here [Music] [Music] you

Channel: Necroware

Views: 14,453

Keywords: retro, hardware, soldering, repair, review, nerd

Id: DKLKtH_rQJU

Length: 23min 37sec (1417 seconds)

Published: Wed Nov 04 2020