Question about oscilloscopes for audio

[PPP]

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!

 

[Eeyore]

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?

That depends if you reckon you can *see* to 16 bit resolution ! I certainly
can't.

What do you want to use the scope to do ? Just view stuff or measure ?

Graham

 

[PPP]

I'd like to measure the audio signals as it passes from different op
amp stages.

 

[Joel Kolstad]

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.

The terminology is a little misleading here. It's useful to digitize audio
signals to 16 bits -- and your ear can certainly tell the difference between
8 bits and 16 -- but for *viewing* a signal you probably aren't going to get
much useful information out of more than 8 bits unless you have a device
(newer digital scopes, a spectrum analyzer, etc.) that can display, e.g.,
log(input signal) (in other words, can display the input signal in dB).

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?

For a headphone amplifier you'll be able to perform design & troubleshooting
just fine with an 8 bit scope. If you're building a very high accuracy
amplifier, however, you'll need something better once it's finished to
measure, e.g., total harmonic distortion.

Note that many (even most) low cost "16 bits" oscilloscopes will not actually
achieve 16 bits of resolution without a *huge* amount of averaging -- 16 bits
is over 100dB dynamic range, which doesn't go together with "wideband" and
"cheap."

---Joel

 

[Eeyore]

I'd like to measure the audio signals as it passes from different op
amp stages.

Measure as in use the oscilloscope to measure - does it have the inbuilt ability
to do this ?

Please don't top-post btw.

Graham

 

[neon]

actualy 64 bits is much better. My question why don't you use an analog scope it is much slower cheaper and infinity of bits and see actual signal. there is quite a difference between analog and digital scopes. and the difference is applications in your case analog is the way to go.

 

[PPP]

For a headphone amplifier you'll be able to perform design & troubleshooting
just fine with an 8 bit scope. If you're building a very high accuracy
amplifier, however, you'll need something better once it's finished to
measure, e.g., total harmonic distortion.

Ahh, I see. But isn't total harmonic distortion always an important
factor in audio design? Personally, I don't mind a little distortion as
long as I can still enjoy the audio.

Note that many (even most) low cost "16 bits" oscilloscopes will not actually
achieve 16 bits of resolution without a *huge* amount of averaging -- 16 bits
is over 100dB dynamic range, which doesn't go together with "wideband" and
"cheap."

Thanks, Joel!

 

[PPP]

Measure as in use the oscilloscope to measure - does it have the inbuilt ability
to do this ?

Well, I wanted to visualize the waveform and its distortion. At the
same time measure its amplitude.

Please don't top-post btw.

Sorry. Thanks, Graham!

 

[Harry Dellamano]

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!

This is what works for me. A USB audio interface unit for your PC, a good
one is the M-Audio Audiophile -USB found here for $150.
http://www.fullcompass.com/product/255063.html
This will give you 2 input channels and 2 output channels of 24 bit- 96KHz
performance, fully isolated.
Then get a software package to interpret and display the data on your PC in
scope or spectrum formats. Here is a good one for $100.
http://www.trueaudio.com/index.htm
This setup will output sine waves with harmonics down >90db and has an
input noise floor of -110db at 1.0KHz and will do a full frequency response
with one keystroke in <1.0 second. Perfect for headphone design. I am
designing transcutaneous power and data transfer for implanted hearing aids
using this setup.
Sorry for the plug but I am looking for more work in the medical arena,
power electronics gets boring after awhile.
Cheers,
Harry

 

[Eeyore]

Ahh, I see. But isn't total harmonic distortion always an important
factor in audio design? Personally, I don't mind a little distortion as
long as I can still enjoy the audio.

There are various types of distortion. Some are quite benign yet some are highly
objectionable. A simple percentage figure is not an accurate guide.


Graham

 

[Eeyore]

Well, I wanted to visualize the waveform and its distortion. At the
same time measure its amplitude.

Unless it's *horribly* distorted it really won't be visible on a scope. You really
don't want to listen to clipping !

Sorry. Thanks, Graham!

No problem.

Graham

 

[[email protected]]

Harry Dellamano schreef:

This is what works for me. A USB audio interface unit for your PC, a good
one is the M-Audio Audiophile -USB found here for $150.
http://www.fullcompass.com/product/255063.html
This will give you 2 input channels and 2 output channels of 24 bit- 96KHz
performance, fully isolated.
Then get a software package to interpret and display the data on your PC in
scope or spectrum formats. Here is a good one for $100.
http://www.trueaudio.com/index.htm
This setup will output sine waves with harmonics down >90db and has an
input noise floor of -110db at 1.0KHz and will do a full frequency response
with one keystroke in <1.0 second. Perfect for headphone design. I am
designing transcutaneous power and data transfer for implanted hearing aids
using this setup.
Sorry for the plug but I am looking for more work in the medical arena,
power electronics gets boring after awhile.
Cheers,
Harry

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...

 

[colin]

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?

8 bits is just about ok for a scope I gues,
just about the thicknes of the trace line I gues,
although if it has zoom and other functions this makes it a bit limited.

But if you realy need to do much more than just look at the basic shape
then maybe you need something more than a scope.

Colin =^.^=

 

[Michael A. Terrell]

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...

Its all Johnny Cash's fault! After all, he got it "One piece at a
time", instead of all in one piece. ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Stanislaw Flatto]

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...

Memories!
And singers had to 'know' how to talk (spell) before beeing sicked
against audience.

Have fun

Stanislaw

 

[Phil Allison]

"PPP


** Groper alert !

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?

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

Typically dual trace with 20 MHz vertical bandwidth or more.

Are none available in your lab ???

Using either 8 bit digital scopes or a PC soundcard as makeshift audio scope
is plain dumb - the former suffer from poor image quality and aliasing
while the latter has insufficient bandwidth for what you intend doing.




........ Phil

 

[PeteS]

"PPP


** Groper alert !





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

Typically dual trace with 20 MHz vertical bandwidth or more.

Are none available in your lab ???

Using either 8 bit digital scopes or a PC soundcard as makeshift audio scope
is plain dumb - the former suffer from poor image quality and aliasing
while the latter has insufficient bandwidth for what you intend doing.




....... Phil

I am in complete agreement with Phil on this. An Analogue scope with
20MHz bandwidth can be had for relative peanuts and is indispensible for
this sort of work.

Cheers

PeteS

 

[Eeyore]

I am in complete agreement with Phil on this. An Analogue scope with
20MHz bandwidth can be had for relative peanuts and is indispensible for
this sort of work.

Cheers

PeteS

Count me in on these remarks too.

Graham

 

[David L. Jones]

"PPP


** Groper alert !





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

Typically dual trace with 20 MHz vertical bandwidth or more.

Are none available in your lab ???

Using either 8 bit digital scopes or a PC soundcard as makeshift audio scope
is plain dumb - the former suffer from poor image quality and aliasing
while the latter has insufficient bandwidth for what you intend doing.

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

 

[Ben Bradley]

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.

This "higher accuracy" is so that software can make FFT out of the
signals that accurately show signals 90dB below the max (for showing
low levels of harmonic distortion), neccesary for testing high-quality
audio systems. FFT's from 8-bit scopes can show at most 40 or 50 dB
below a max signal.

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?

The truth is, there were pretty good headphone amplifiers made
before there were 16-bit analog-to-digital converters. But if you want
to test your amp for the lowest distortion using the easiest and most
convenient way, you should use one of these:

* An oscillocope with 16-bit vertical input and FFT capability (I'm
not familiar with any 16-bit models, and like in your lab, all the
ones I've used are 8-bit).

* The M-Audio or similar interface and a PC with appropriate software
such as http://audio.rightmark.org/products/rmaa.shtml)

* A hardware system made just for the purpose such as an Audio
Precision system (http://ap.com/).

There are other, analog ways to measure distortion, but these
systems make it about as easy as hooking things up and pushing a
button.

On the other hand, you likely won't need these to make your amp.
Just put it together and if there's no obvious distortion (in your ear
or shown on an 8-bit or analog scope), then you almost surely did it
right.