Audio signal generator

[travis]

ok heres the deal - what i want to do is make a circuit that when a switch is closd will pass a audio signal to a speaker

the end goal of this is to make a simulated bass drum by which when the kick pedal activates the switch a bassy 'doof' type sound will be sent to a subwoofer.

if anyone can give me a bit more understanding in this topic of how a simple audio signal can be created or point me to somewhere for some info i will be greatly appreciative.
cheers
travis

[Guest Yevgenip]

What type of sound do you want to make? A singal tone? if so, what is the frequency?

[audioguru]

Hi Travis,
Welcome to our forum.
You probably need a bandpass filter circuit that has its gain set just below feedback. Your kick pedal switch would send it a DC pulse and it will ring at its set frequency and slowly decay away, just like a real drum. You could even have pushbuttons or a knob to change its frequency, even a sweep frequency change! BoooooooO-OO-OO-OOM! ;D

You can't simply gate an audio oscillator on and off. Then it would sound like a car horn, but at a lower frequency. Beep, beep. ;D

[MP]

Travis,
What you are looking for is a VCO (Voltage controlled Oscillator) circuit to make your tone. This should then be controlled by a VCA (Voltage Controlled Amp) to change the amplification. A more advanced type of VCA is an envelope generator. This will change the amplification characteristics of the sound wave. The sound wave can be divided into 4 parametrers: Attack, Decay, Sustain, and Release, or commonly known as ADSR. By changing the ADSR of any sound, you can make it sound like a different instrument. For example, you can make a piano sound like a guitar or flute, etc. This is the principle that is used in sysnthesizers.
How does this knowledge help you? You will want to use this principle to make your tone sound like a drum.
PAIA electronics used to sell lots of different do-it-yourself synthesizer modules. You can still find information and schematics on the web for their products. By the way, if you only want a drum sound, you can get by with an AR envelope filter instead of ADSR.
If you do not find anything on the web, let me know.

MP

[travis]

ok so iv had a look around on the net and this is my understanding.

@ audioguru - your suggestion seems the simplest and as you said works "just like a real drum"

Q) does a 'bandpass filter' circuit still need an oscillator or does it do it all itself? u just turn it on and it outputs a slowly decaying wave of a preset or variable freq.

@ MP - this method seems more involved but the thing i like about it is i can fully customise the sound output

so what i dont understand with this one is how does it make a decaying sound like a drum
if the oscillator puts out a signal (like a sine wave i presume) then the envelope generator changes the waveform to make it sound like a drum - that gives you the drum skin moving up and down but how does it decay

on monday ill go look at the local electronic store and see what DIY kits they have

[audioguru]

Hi Travis,
My "ringing bandpass filter" idea is a bandpass filter like used in a sine-wave oscillator but its gain is set to just below the amount necessary to sustain oscillation. Its frequency is set with 2 resistors that can be switched or controlled with a dual pot like a stereo volume control part. It is commonly used to make "bongo drums" but in your case it would have a lower frequency to sound like a bass drum. This simple circuit would have a fast attack and slow decay envelope, just like a real drum. You might find a bongo drum kit in which you can increase the value of its two frequency-determining resistors or capacitors. Try a Google search for "bass drum circuit kit" or "bongo drums circuit kit".

[travis]

ok so i still dont get the VCO - VCA method that MP sugested - i think its the way id like to go but i need to understand whats going on better so i can get the components i need together

a) i need an VCO - the local electronic shop has a "wave generator" kit the specs are:
Freq range 10Hz to 100kHz
Both amp. and freq. are voltage controlled
On-board voltage regulation ensures good stability

is this the sort of thing i want? can u give me some schematics of a simple one that suits my needs

b) is the only other thing i need is a VCA - id liek to try and use an envelope generator so if u can again give me some schmeatics to one thats just enought to suit my needs

i live in australia so iv never heard of PAIA(i assume there not australian)

the last thing is im not 100% on how the two units go together to give me the sound im after can u give me a brief overveiw on it

thanks alot for the help sofar
travis

[audioguru]

Hi Travis,
Voltage Control adds complication to your electronic drums project. Most VCO's have a continuous pulse or square-wave output that sounds like a "BUZZ", not a smooth sine-wave sound from a real drum. Therefore in addition to requiring a VCA or Envelope Generator to control its attack and decay, a VCO will need a complicated sine-wave shaping circuit.

You don't need Voltage Control unless you quit playing and let a computer do it instead. A simple circuit like I described can be easily controlled with switches or pots if required.

I made a quick search on Google for a simple circuit like has appeared in magazines over the years, but I couldn't find one for you. Maybe your search will be successful.

[travis]

ok so heres the deal i went to the electronics shop and brought a sine / square oscillator kit goes from like 2hz to 20khz i think it outputs from like 0v to 2v (amplitude of wave) cant remeber much else bout it atm.

iv nearly finished putting it together the next thing is getting a envelope generator but i dont think they have a kit like that at the shop so i need some places to look for some plans / schematics the problem im having is finding one that suits my needs as i dont know whats what.

side note - i need to be able to mesure the freq of the wave to tune it up so it runs properly - can i plug the output of the vco into my computer and use a program to read it? - ie. anyone got a suggestion for a program i could use - eg a ocsilloscope program
p.s. i just saw add up top so ill check that out