Tools of The Trade: Oscilloscope

[amirm]

Audio equipment is tested and evaluated using various instruments. Over time I plan to cover what they do and how they work. As luck would have it, my favorite electronics blogger Dave Jones just did a high-level introduction to oscilloscopes. These are complicated looking instruments but their core is rather simple. Their use in design of audio equipment is essential but in evaluation of their performance, not as much. Still, it is good to know what they are and this short intro video does a great job of that:

 

[Cosmik]

I was given my first oscilloscope when I was about 12! It was ancient even then, valve-based not transistors. I didn't really know what to do with it at first, but over the years it became very useful - I managed to avoid electrocution. I use a USB-based version these days.

 

[RayDunzl]

When I was a kid, we had TheTube.

I still fondly remember my host, Truman Bradley:

 

[amirm]

When I was a kid, we had TheTube.

I still fondly remember my host, Truman Bradley:

Lovely episode. Note how they speak so clearly!

 

[RayDunzl]

I like to see the Lissajous.

Musical Rorschach.

M. Zillch posted this:

I figure the vinyl playback system is not quite SOTA, in this case.

 

[Speedskater]

I have a Heathkit Audio Scope AD-1013 that does Lissajous patterns. Don't know if it still works.

 

[amirm]

M. Zillch posted this:

I figure the vinyl playback system is not quite SOTA, in this case.

I had seen that but did not realize it was produced by Alan Shaw of Harbeth (speakers) in UK. They have their own forum with a long thread on the topic: http://www.harbeth.co.uk/usergroup/...praisal-of-vinyl-v-digital-romance-v-reality/

Back to oscilloscope, in this situation where massive amplitude variations exist, the instrument does make a good tool in seeing the difference between CD and LP. A spectrum analysis would be a lot more revealing but not necessary given how degraded the LP is.

And yes, I suspect it is not a high-end LP player but how good do they produce pure tones regardless of price?

 

[Don Hills]

Not too well.
http://archimago.blogspot.com.au/2014/08/measurements-technics-sl-1200-m3d-wow.html
http://archimago.blogspot.com.au/2014/11/measurements-roksan-tms-1-wow-flutter.html
http://archimago.blogspot.com.au/2014/09/measurements-digital-audio-and.html

I would like to see someone with a really high-end vinyl rig and a good ADC record the 1 KHz test track off a test LP and post it online. In the past I've done this live as a "party trick", at listening sessions where vinylphiles made claims for their turntable's performance, I played the track off the test record and then the same tone from a test CD. I then pointed out that the imperfctions heard in the vinyl version were present in all music played on that turntable...

 

[NorthSky]

 

[amirm]

That is impressive high frequency/ultrasonic response in favor of LP.

 

[DonH56]

I assume many remember the quadraphonic LPs that used an ultrasonic (30 kHz) carrier. I have measured >60 kHz on an LP, even >100 kHz but it was essentially noise. When the CD first came out that once one of the things the detractors used, their limited upper frequency band compared to LPs. They didn't talk much about the ability to play well below 20 Hz without rotational noise from warps and such, LF motor rumble, etc. and nor did they appreciate the CD's much greater dynamic range. That was when a lot of preamps and amps were touting 100 kHz bandwidth as necessary for high fidelity, hearing acuity and tweeters be durned. The "key jingle" test was popular, never mind that testing showed nobody could tell when those ultrasonics were rolled off...

 

[NorthSky]

If frequency response is an important element of music listening, then the LP is much ahead. The CD in comparison hits a brick wall and falls dead @ 20-22 kHz.

But there is more than frequency response in music; there is dynamics, attacks, bass punches, highs clarity, sweet mids.
After live, from personal experience, R2R tapes retain the closeness best.

And between CDs and LPs @ both 33 1/3 and 45, it's a question of the gear used and the music recording playing.
CD players are easier to setup and adjust, but other things varied, from the people who designed them and the parts they used inside and what they do to the overall sound...jitter, dither, sampling, filtering, re-sampling, processing, demodulating, compensating, pulsating, decompressing...

Turntables are the music art; they require love, adjusting, romance, care, affection and compensation.

It's funny how easily our brain is influenced. But music without fine tuning is incomplete, like many paintings that are selling unfinished but no one notices.
Only when the brush of the master has completely stopped, and the painting is installed in his frame and exposed to the gallery's wall for sale, only then when it is sold and goes in another one's room (the buyer, art collector), and that the painter has no easy access anymore to apply some final touches (some painters do, their paintings are never finished), that's the moment frozen in time in its final resting space.
It is very similar with music.

Yeah, an oscilloscope can show us that. ...That's when listening stops, and analysing starts.
By the way, in that last video above...the CD sounds much more dynamic, more full and punchy, with energy and rhythm.
The LP might have more extension in the audio spectrum, but it sounds congested, thin, lacking verve, musical strength.
That's from the video, an old inexpensive CD player, and an inexpensive turntable.

Yes, the LP is much more extended in the graph, but the sound is more alive from the CD.

So what measures better is not necessarily what sounds better. Digital is euphonic, analog is euphoric.

 

[Sal1950]

Lovely episode. Note how they speak so clearly!

Yep, I easily understand every word. As opposed to today when I keep punching the remotes repeat button and after three times give up when I still can't make out the lines.

 

[RayDunzl]

... and another

"Information:

• What is this? Music visualized through an oscilloscope. Basically "drawing with sound" (vector graphics with X/Y coordinates, made from L/R audio channels). The images you see are created with the exact same waveforms that you hear. The left audio channel is used for horizontal deflection and the right channel for vertical deflection of the oscilloscope's cathode ray."

I think he has a Z-axis in there too, for blanking/brightness.

 

[Cosmik]

If I fed an audio signal into a nonlinear network (say resistor/diode to create some distortion) I am sure it would create a lovely spread of mush going all the way out to 60 kHz and beyond. Some people would even say it sounded better.

 

[Speedskater]

If we had a test LP with sine-way tones stepped at 1kHz all the way up to 30kHz and then played it back on 3 different cartridge, tone-arm, pre-amp combinations. I think that the high frequency response curves would be all over the map. Looking more like a roller-coaster than a smooth curve.

 

[NorthSky]

Speaking of phono cartridges, can we measure them with an oscilloscope?
And, the ultra high end (expensive) ones, hand-made individually/separately; do they exhibit variations between one and another of the same?
...Auditory and measurably.

 

[amirm]

Sure. We can measure their output with a scope (short for oscilloscope). And can also do the same in frequency domain. The trick would be a high quality LP to run under them.

 

[Don Hills]

It used to be commonplace to measure cartridge frequency response in reviews, using a sine sweep test disc.
The main takeaways for me were the in-band response variations and the cantilever resonance breakup points, usually in the 19 to 22 KHz range.

 

[RayDunzl]

If we had a test LP with sine-way tones stepped at 1kHz all the way up to 30kHz and then played it back on 3 different cartridge, tone-arm, pre-amp combinations. I think that the high frequency response curves would be all over the map. Looking more like a roller-coaster than a smooth curve.

In another thread there are some LP Rip vs CD spectrums, seems like they looked pretty close to me.

Now to find them...

http://audiosciencereview.com/forum/index.php?threads/lp-sound-vs-digital.76/

And it looks like TBone has the ability to pursue new measurements:

http://audiosciencereview.com/forum/index.php?threads/lp-info-loss-w-repeated-plays.414/