Question about oscilloscopes for audio

[qrk]

Aliasing is a thing of the past now that virtually all DSO's (even the
low end ones) use real-time sampling (usually >10 times the bandwidth)
instead of repetitive sampling.

But yeah, agreed, a regular analog scope is what you need here.

Dave

I still have problems, on rare occasions, getting a modern DSO to
behave due to aliasing issues. Usually turn on the analog scope to
figure out what I'm looking at then set up the DSO accordingly.

For audio, noise, and odd digital problems analog scopes are the way
to go. If you need to measure distortion, use a decent spectrum or
distortion analyzer.

 

[GregS]

I still have problems, on rare occasions, getting a modern DSO to
behave due to aliasing issues. Usually turn on the analog scope to
figure out what I'm looking at then set up the DSO accordingly.

For audio, noise, and odd digital problems analog scopes are the way
to go. If you need to measure distortion, use a decent spectrum or
distortion analyzer.

I have and use analog scopes but also have and use combination
analog and digital scopes. I have an old Phillips PM3350A
and often recommend the Hameg combination scopes with
CRT's. HM507. I think they deleted a cheaper model
with less bandwidth.

More bandwiths is useless, but more samples is good, as well as at least 12 bit vertical resolution
minimum if you have to use digital.

greg


greg

 

[john jardine]

I still have problems, on rare occasions, getting a modern DSO to
behave due to aliasing issues. Usually turn on the analog scope to
figure out what I'm looking at then set up the DSO accordingly.

For audio, noise, and odd digital problems analog scopes are the way
to go. If you need to measure distortion, use a decent spectrum or
distortion analyzer.

At a customers last week, had to use their new, Tek TDS3024 'scope. Must
admit to being somewhat leery due to a previous time waste with a HP model.
Yep!, right on cue the damned thing refused to display a 100Hz, 15V, 20uS
signal.
It looks like a girls handbag and about as much use
john

 

[Harry Dellamano]

Harry Dellamano schreef:


Harry, your posting sort of baffled me, I had it in the newsreader,
then decided to erase it and convince myself I had never seen it

There are several reason for wanting to do that, first I started
wondering
'What headphone has 110dB range, my Sensheiser HD201 does not dampen
for example room (PC fan) noise enough to get to that, given distortion
at the upper end'.
Then why all the expensive stuff, while every PC has a 16 bits
soundcard, and programs
that are free like 'oscope' (Linux) exist, also there are free fft
packages.

Realy I have done audio with a normal analog scope and may still prefer
it to a digital
one in some cases.
As to 16 bits scopes, OK, lets say most sensitive range is 10mV (1mV
for a good
analog audio scope existed too) per division.
So if 10 divisions on the graticule, 100mV, and 65536 steps (2^16), the
lowest signal
would be 1.525 MICRO Volt.
Now maybe somebody here can make a headphone amp with that low noise,
but I cannot.

So that is why I wanted to forget about what you wrote, but something
in me looked it
up in google (sorry if google reformat my text in weird ways), and as
I am very old, maybe I
have been missing some important new audio topics.

Hell you can get a good idea about distortion simply by substraction
output from input.
And since mp3 nobody hears anything anyways.
There were days of HiFi and .000001 % (;-)) harmonic and crossover
distortion,
but since the appearance of the 10 cc PC speaker I am not sure it makes
a difference.

So, for what it is worth: And you can take a metal screw, drill it in
the skull,
wind some coper wire over it, bias with a magnet.... just like chewing
cookies.
(This last sentence was a joke OK A JOKE).
Pfff.

So please correct my simplistic audio views if you find thse flwaed.
But in my days audio sounded a lot better then mp3 on PC speakers.
24 bit, 48 bit or whatever...

Sorry if my post baffled you, I am known to do that. A post by Ben Bradley
in this thread said best what I was trying to relate. You do need a scope
for design of audio equipment but for final test and verification your
client my need data in the frequency domain. Using a PC based sound card
normally has high audio and EMI noise levels. The USB sound card that I
proposed is at the end of a 5 meter cable and electrically isolated from the
host PC. This allows gain and distortion measurements from any node in your
DUT. The -110dbu noise levels are nice even if you only require -50dbu. The
software I suggested controls output waveforms and crunches input data
yielding great printable curves of the DUT's performance.
YMMV
Harry

 

[Don Lancaster]

At a customers last week, had to use their new, Tek TDS3024 'scope. Must
admit to being somewhat leery due to a previous time waste with a HP model.
Yep!, right on cue the damned thing refused to display a 100Hz, 15V, 20uS
signal.
It looks like a girls handbag and about as much use
john

The myth continues through many generations that HP knew how to build
oscilloscopes.

Their last decent scope was the 130C.
It has been stadily downhill ever since.



--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[David L. Jones]

There is a special button on the scope just for such occasions, it's
called "Autoset".
Students today make extensive use of it ;-)

The myth continues through many generations that HP knew how to build
oscilloscopes.

Their last decent scope was the 130C.
It has been stadily downhill ever since.

The new Agilent ones are brilliant. The older mixed-signal 54620 series
or the newer 6000 series are just so easy and intuitive to use, and the
6000 series performs as good as an analog scope in most respects.
I've lost count of the number of times people have come to borrow my
Agilent because they couldn't figure out how to drive their Lecroy or
Tek.

Dave

 

[SioL]

It has been stadily downhill ever since.

The rest of their stuff is bad, too. Their all-in-one printers
with hundreds of megabytes (Yes, I am not kidding) of driver
bloatware are horror. Won't print B/W fax without installing
a new colour cartridge first (which by the way was not empty
anyway as I only printed BW faxes).

A bit OT, but had to get it off the chest.

SioL

 

[qrk]

On 15 Nov 2006 17:52:15 -0800, "David L. Jones" <[email protected]>
wrote:

[snippage]

There is a special button on the scope just for such occasions, it's
called "Autoset".
Students today make extensive use of it ;-)

Dave

In John's case, he was looking at a 0.2% duty cycle signal. That's
hard for a digi scope to deal with when looking at a full cycle or
two.

 

[[email protected]]

Hello,

I was reading the oscilloscope tutorial here:
http://www.picotech.com/applications/oscilloscope_tutorial.html

The section regarding vertical resolution specified the following
device:
http://www.picotech.com/audio_spectrum_analyzer.html

Also, from my searches in this group using "audio oscilloscope", I
found the following link:
http://www.syscompdesign.com/oscilloscope.htm

According to the tutorial, it states that for audio signals I should go
for a scope with a higher vertical resolution (16 bits) so I can have a
higher accuracy. However, most of the scopes I've seen including ones
in our university lab are 8 bits. For my application, I'm trying to
duplicate a headphone amplifier, does this mean that the Syscomp Design
(and university lab) scopes would not be suitable for my project?

Thanks!

A distortion analyser plus a scope can be very useful. You are going to
need the distortion analyser for a clean audio source anyway. If you
put the scope on the residual output of the analyser, you can "see" the
source of the distortion. That is, with a dual trace, look at where the
distortion residual signal gets large. If it is near the zero
crossings, then the problem is in the AB stage. If the distortion is
near the peaks, then there are issues related to signal swing or the
stiffness of the power supply.

If you can track down an Audio Precision, that would be the way to go.
Next up in the old HP8903B.

I guess I should mention that once you use the distortion analyser to
knock out the fundamental, then whatever tool you put on the residual
output is now much more useful since you are only looking at the error
of the amp, not the full output of the amp.

 

[PPP]

** Groper alert !

I like Google's interface.

** For audio design and * troubleshooting * work - what you need is a
standard * ANALOGUE * scope.

Are none available in your lab ???

The only lab I have access to have Tektronix DPOs. Maybe I can just use
these scopes for initial design and somehow use a spectrum analyzer (I
also have access to this in another lab) to trouble shoot for THD?

Also, if the bank of mom & pop were to look for some holiday gift,
would the following oscilloscope be suitable :
http://elexp.com/tst_gds2.htm (GDS2202 .. 200MHz, 2 Channel, DSO) ? I
already got a laptop last year for roughly the same price. ;-)

Thanks!

 

[GregS]

I like Google's interface.




The only lab I have access to have Tektronix DPOs. Maybe I can just use
these scopes for initial design and somehow use a spectrum analyzer (I
also have access to this in another lab) to trouble shoot for THD?

Also, if the bank of mom & pop were to look for some holiday gift,
would the following oscilloscope be suitable :
http://elexp.com/tst_gds2.htm (GDS2202 .. 200MHz, 2 Channel, DSO) ? I
already got a laptop last year for roughly the same price. ;-)

I don't know bout these. I don't think any have FFT. I
would go for Tektronix or Hameg. As I said, I like
the HAmeg Analog/Digital scopes. with a push of the button, you can choose.

greg

 

[Eeyore]

The only lab I have access to have Tektronix DPOs. Maybe I can just use
these scopes for initial design and somehow use a spectrum analyzer (I
also have access to this in another lab) to trouble shoot for THD?

How much THD are you looking for ?

It simply won't be visible on a scope trace at levels that are audibly
significant.

Graham