Oscilloscope Music

I have a Tek 410A digital scope and a small SC-504 60mHz analog. I don't know how good the sound card is in my lab computer, but I have a Mark of the Unicorn 8 channel audio interface in my wife's studio computer that should do the trick. I'll be sure to check it out.

If the cheap headphone converters have a DC offset, can't you just set the scope for AC coupling?

It's one thing to watch a Youtube video of it. It's entirely different to watch it on your own oscilloscope.

"Planet" is one of the tracks you get for your €5.

The MOTU unit I have will go to 24bit/96kHz, on eight channels at the same time, although I never tried it there. Everything I've used it for was at 16/44.1 - 8 channel. I guess this will be my chance to try it out.

Now that was fascinating?..

With all the ultrasonic frequencies in the audio program material, I would be afraid to play this on a decent sound system for fear of burning out the tweeters.

It may be wise to run the full bandwidth audio to the scope but pass the speaker audio through a low pass filter first.

It doesn't even really work with MP3. The music directly controls the position of the glowing dot on the screen. As soon as you introduces "losses", the position of the dot isn't accurate any more so the picture is drawn wrong. Losses are either caused by compression based on losses (MP3) by leaving out signal components you can't hear anyway or leaving out samples when your sound card can't play the samples fast enough. This is based on 192kHz sampling frequencies, common hardware can only play "CD quality" which is 44.1kHz or "studio quality" which is 48kHz. Also common sound gear can't reproduce DC components since audio is pure AC, DC can't be heard at all. You need DC to draw straight horizontal or vertical lines.

The 192kHz standard is nothing but a bare digital-to-analogue converter which is rather fast for audio. It is lacking filters to eliminate DC since they are not necessary because the signal is fine enough to play audio without any distortions you could hear. The CD standard is not capable to do that. The audio signal is sampled in 16 bits, 65536 different voltages levels. Even changing between single steps causes a significant "step", a jump in the voltage which appears as a high pitched click. Analogue filters eliminate anything above 20kHz. In reality since good analogue filters are expensive, a common CD player usually starts to suppress above 16kHz.

Since a CD SHOULD be able to reproduce 20kHz since 44.1kHz sampling frequency gives you 22.05kHz in theory, either the CD player includes very expensive analogue filters (about $200 extra in the early days, nowadays still $20 extra!) or must use another way to solve the problem.

The first inexpensive players capable to reproduce up to 20kHz (and more) were the "1-bit DAC" ones. They recalculated the audio data to create 1-bit samples but with 1MHz frequency. The output of the DAC (Digital to Analogue Converter) is either "on" or "off", a simple, inexpensive circuit. By clicking it on and off so rapidly (up to 1MHz), the immense noise caused by this method is far over the spectrum you can hear, several hundred kHz at least! This reduces the costs of the DAC itself which is just a simple electronic switch and the analogue filter circuits which is basically nothing more than a capacitor and a resistor or two. The analogue part of the player is as inexpensive as it can be but it requires a rather powerful processor. Nowadays such a processor is less than 10 cents.

Nowadays, CD/DVD players for audiophile people are 192kHz. They recalculate the data as well, but use 32-bit resolution and 192kHz sampling frequency. The reason is that a >10-MHz DAC has become real cheap since used inside a lot of stuff like printers, digital cameras, cell phones, telephone circuits, TVs and many other things. Also processing power has become real cheap, too. What was a "state of the art" PC about 15 years ago now fits into a 5 cent chip!

So this is where this 192kHz "nonsense" audio standard comes from. Originally just a way to reproduce a CD with the best quality possible but on very inexpensive hardware. This was then adopted to sound cards capable to play (and record) 192kHz data directly. It doesn't really make any sense since most people don't use CDs any more and play MP3s.

So if you have a very good stereo system and want the maximum quality, theny buy a 192kHz audio CD/DVD player and buy music DVDs to feed it. It makes no sense with a sound card or USB-headphone converter at all - unless you play music for oscilloscopes...



And here is what MIDI is:

MIDI is 1980s technology, absolutely incapable to convey any form of useful sound at all! The data rate is 31250 k/bit which would translate to mono, 2kHz maximum. Not even enough for simple speech. Even with MP3 compression, the best you can do is to use it as a lousy Dictaphone or maybe an answering machine if you don't mind that you can't really recognize the owner of the voices.

MIDI is basically like a sheet of notes. It is music, but not a recording of actual music at all. It is a set of instructions how to play the music on (digital) instruments.

A MIDI keyboard for example will report which key you press, (how hard) and how long. To hear something, a MIDI module is required which they plays the actual tunes controlled by the data from the keyboard. Most MIDI keyboards have the module (and speakers) built in so you can play music on them directly. But you can also plug in a better module or record the data on a MIDI sequencer. A sequencer can record and play back which keys you press on a keyboard or play MIDI "music sheets" made by someone else or typed from actual music sheets. Some MIDI keyboards include a sequencer. But any computer with a MIDI interface can also be a sequencer.

MIDI in computer sound cards is actually just a MIDI module with the PC acting as the sequencer. Early computer games used MIDI since there was not enough memory available to play recorded music and sounds. E.g. DOOM or DUKE3D played their in game music as MIDI and the F/X (gunshots) were tiny sound samples.

If you have a good MIDI module, you can still use it. There are USB to MIDI converters out there which will work with any modern OS. Using the DOSBOX emulator, you can hook your MIDI module (or keyboard with built in module) to your computer and enjoy old DOS games with really good music quality. The quality of the Soundblaster cards was not good at all. There is a HUGE difference in sound quality and complexity. A lot of games could play much more instruments when hooked to a "general MIDI" or "Roland MT-32 compatible" sound module than when played on an ordinary sound card (Adlib or Soundblaster). Even modern sound cards which can't play any MIDI and use software emulation are very low quality compared to using a real MIDI module.

So if you own a MIDI module (or keyboard), use an USB converter and set the DOSBOX emulator to "general MIDI", then select "Roland MT32" or "general MIDI" in the settings of the DOS Game.
If you own the classic MT-32, it will also display some texts on its display when playing Sierra Games.

Many newer MIDI devices don't even have the 5-pin MIDI connector on them anymore. My wife recently got a ROLI MIDI controller keyboard. It has a USB connection on it but no MIDI connectors at all. It still outputs the MIDI standard data but over USB. A problem using USB for MIDI is that it doesn't provide ground isolation. The MIDI hardware specification calls for optical isolation between MIDI devices. When we would connect my wife's digital piano to the computer running the DAW software, you could hear all kinds of digital noise coming out the analog audio output of the piano. They sell USB optical isolators where even the 5 volt USB power output is isolated. One of those completely cleaned up our noise problem.

Interesting that you mention the Roland MT-32. That was the first MIDI synthesizer module that we owned. We got it in the late 80's for around $500. We still have it and sometimes actually use it as there are a couple of instrument voices on it that my wife really likes. The one we have is the older version without the headphone jack.

The ROLI keyboard is rather unique. Not only can you play between the keys, but if you slide your finger up and down a key, it will change the MIDI continues controller data that you assign to that MIDI channel. It opens up a whole new world of possibilities for a keyboard player. ROLI also has some rather unique ways of getting around the MIDI specification limitations, like being able to pitch bend just one note while holding others steady.

SD will love this. ROLI keyboard simulating an electric guitar sound.




And it can do a lot more than simulating just guitar. Where you press a key and how hard you press it can determine what sound you get. Here they have the lower part of the keys sounding string voices and the upper part of the keys, brass. Listen to what happens when he slides his fingers up the keys.

"I may have to get me one of them"..... aww "duck", I was soo looking towards being able to buy a new powersaw as well?..