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Quality aspects of ADC, Does quality gear makes a difference?
ktf
post Mar 3 2011, 22:45
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Hi all!

Background information (safe to skip rolleyes.gif )
Currently I'm preparing a large archival operation: my musical society has a collection of recordings on compact cassettes from 1980 to 1990, about 140, which I think have to be digitalized to protect them from deteriorating. I have found a nice tape deck (Nakamichi DR-3) but it has to stay at the office of the executive committee. A friend of mine has a nice ADC for this job, a quality portable mixing console with USB out, but it cannot stay at the office as it is more or less public and he doesn't trust everyone there. However, it is too much hassle to bring it every time, as I think this operation will cost about a year: 3 recordings a week. So, I guess I'm stuck with my own ADC: a Creative X-Fi Surround 5.1 USB-card, which is not really made for the job, but I can at least leave it at the office, as it isn't that valuable.

On-topic
That friend of mine that offered me his portable mixing-console with ADC argued that with a cheap ADC all little nuances and details would vanish, so I should look for another solution than using my Creative ADC. That made me think: i'm much more a theoretician than he is, so I was wondering, what makes a high quality ADC? I know the working principle of several ADCs, I can't imagine which link in the chain would be capable of 'erasing details' anyway. How does a non-linearity in an ADC sounds like in practice? And jitter? I guess uncorrelated, random jitter could sound like 'more noise', as it is random. To me it seems a low-quality ADC doesn't add anything but noise and a non-linearity, let alone it could remove things from the signal.

In short: what could a low-quality ADC do with the signal except adding noise? Probably I'm far too short sighted, can anyone enlighten me?


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Arnold B. Kruege...
post Mar 8 2011, 13:38
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QUOTE (ktf @ Mar 3 2011, 16:45) *
That friend of mine that offered me his portable mixing-console with ADC argued that with a cheap ADC all little nuances and details would vanish,


Your friend is drinking the High End Audio Kool Aid. ;-)

QUOTE
so I should look for another solution than using my Creative ADC.


Many of us have been down that road.

We've all learned that once audio gear meets certain technical standards, it all sounds the same. What has changed over the years is that the cost and size of audio gear that meets certain standards has decreased dramatically.

In 1970 the university I attended bought a 200KHz sample rate 16 bit ADC/DAC. I seem to recall that it cost about a half million dollars and filled a full height 19 inch rack cabinet. Last year I bought a USB audio interface that outperformed it, and had twice as many channels. I got change from $100. I could fit it in my hand but if I closed my hand the corners of the box showed. But, the box it was in was mostly empty, whereas that 1970 DAC was packed full of circuits.

QUOTE
That made me think: I'm much more a theoretician than he is, so I was wondering, what makes a high quality ADC?


A quality DAC provides basic clean signal processing, IOW low noise and distortion. It is also durable and convenient to use. All failures to provide clean signal processing can be broken down into noise, linear distortion and nonlinear distortion. You may be unfamiliar with the oxymoron-sounding phrase "Linear distortion" but that is just more familiar things like flat frequency response and appropriate phase response.

QUOTE
I know the working principle of several ADCs, I can't imagine which link in the chain would be capable of 'erasing details' anyway.


Elsewhere on HA we've been discussing just that. I don't know how to erase details with equipment that meets fairly ordinary technical standards. About as close as we can get is to bury small signals in noise.

QUOTE
How does a non-linearity in an ADC sounds like in practice?


Nonlinearity adds tones to sounds that weren't originally there. The added tones are both harmonics and also sum and difference tones related to the tones in the original recording. The harmonics tend to fit in with the harmonics that are already in the music. The sum+difference tones don't fit in nearly as well, and there's no way to avoid them if the equipment is nonlinear. In small quantities nonlinear distortion tends to alter the balance between fundamental tones and the natural harmonics that are in the music. If small enough, added harmonics can be easily ignored or overlooked. They may even make things sound better to some people. The sum and difference tones don't fit into the natural harmonic structure of the music, and tend to give a sort of sour or gritty sound.

For example, if you want people to overlook modest amounts of nonlinear distortion in a demo, you might use recordings of a solo instruments or a certain kind of voice. There won't be a lot of different concurrent tones in the music, and most of the distortion will come out as harmonics which might be overlooked or even preferred. If you want a listening test that is very critical of nonlinear distortion, you might pick a complex sound like a choir. Choirs are particularly good because their signal is dense in the midrange, but leave a lot of less-used frequencies at the extremes. Any sum and different tones that are created will be more audible when they naturally fall into the frequencies where the basic music is less dense.

QUOTE
And jitter?


Jitter is just another kind of nonlinear distortion. In large amounts low frequency jitter is just vibrato or flutter or wow. Which makes a point - while jitter is commonly obsessed over as applying to digital equipment, we've had tons of it for years in LP recording and playback, as well as analog tape. High frequency jitter can be more like an increase in background noise. High frequency jitter has been around for years as "scrape flutter" in analog tape recorders.

The real kicker is that the best analog playback system has tons more jitter than even a mediocre digital system.

QUOTE
I guess uncorrelated, random jitter could sound like 'more noise', as it is random.


Yes, I just covered that, but much jitter is correlated. It is due to interference caused by the signal itself or outside influences like the power line or frame size in digital media. Making jitter go away in a digital system is very simple. Every CD player's optical pickup delivers a massively jittered signal to its decoding electronics. All you do is buffer it and reclock it and its as pure as the clock you use to reclock it. BTW, adequately clean digital clocks are now about a dime a dozen.

QUOTE
To me it seems a low-quality ADC doesn't add anything but noise and a non-linearity, let alone it could remove things from the signal.


The noise and the nonlinearities could add sounds that mask the detail in the signal. Thing is that even inexpensive DACs such as the one in cheap digital music players such as the Sansa Clip, or the motherboard audio interface in your computer, are now really very good. They are capable of sonic transparency, which is the ability to reproduce sound without adding anything that makes it sound different, even in terms of the smallest things that we can reliably hear, or sense in any way.

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ktf
post Mar 8 2011, 18:02
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QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
We've all learned that once audio gear meets certain technical standards, it all sounds the same. What has changed over the years is that the cost and size of audio gear that meets certain standards has decreased dramatically.
(...)
Thing is that even inexpensive DACs such as the one in cheap digital music players such as the Sansa Clip, or the motherboard audio interface in your computer, are now really very good. They are capable of sonic transparency, which is the ability to reproduce sound without adding anything that makes it sound different, even in terms of the smallest things that we can reliably hear, or sense in any way.

I really don't understand how that is possible actually: I study mechanical engineering, in which I'm confronted with the aspects of mass-production. The idea is simple: when something costs more at no benefit, don't use it. I guess a motherboard-manufacturer would choose the cheapest audio-gear it can get: most costumers really don't care, they won't complain about sub-par audio. If they complain, it will be about the DAC, not the ADC, as they do not expect much of those cheap built-in microphones. Placement of these chips won't get a high priority either, as placing and shielding an audio-chip as it should would cost them several dollars I guess, at a budget of ~40 dollar for the whole motherboard, that is not an option. As opposed to what I would expect, computer-audio is certainly not bad, is making audio sound good that easy? I was thinking in a similar way about my Creative X-fi, as it major selling point is surround output, not quality input. Why would they spend a few bucks per unit in getting the ADC right, if (nearly) nobody cares? Why would they meet those minimum quality standards?

In 'professional' equipment, things are different. Specs are read, and if the device doesn't meet the expectations, it will be returned, named and shamed. I can understand why equipment made for the job is well built. I wonder with consumer equipment however, as no one seems to care.

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
Your friend is drinking the High End Audio Kool Aid. ;-)

I'm aware of that. I mentioned him just because he made me think. smile.gif

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
In 1970 the university I attended bought a 200KHz sample rate 16 bit ADC/DAC. I seem to recall that it cost about a half million dollars and filled a full height 19 inch rack cabinet. Last year I bought a USB audio interface that outperformed it, and had twice as many channels. I got change from $100. I could fit it in my hand but if I closed my hand the corners of the box showed. But, the box it was in was mostly empty, whereas that 1970 DAC was packed full of circuits.

I guess that's the blessing of IC's and their miniaturization.

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
A quality DAC provides basic clean signal processing, IOW low noise and distortion. It is also durable and convenient to use. All failures to provide clean signal processing can be broken down into noise, linear distortion and nonlinear distortion. You may be unfamiliar with the oxymoron-sounding phrase "Linear distortion" but that is just more familiar things like flat frequency response and appropriate phase response.

Right, that was what I was after. Thanks!

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
Elsewhere on HA we've been discussing just that. I don't know how to erase details with equipment that meets fairly ordinary technical standards. About as close as we can get is to bury small signals in noise.

I'll take some time to read it smile.gif

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
For example, if you want people to overlook modest amounts of nonlinear distortion in a demo, you might use recordings of a solo instruments or a certain kind of voice. There won't be a lot of different concurrent tones in the music, and most of the distortion will come out as harmonics which might be overlooked or even preferred. If you want a listening test that is very critical of nonlinear distortion, you might pick a complex sound like a choir. Choirs are particularly good because their signal is dense in the midrange, but leave a lot of less-used frequencies at the extremes. Any sum and different tones that are created will be more audible when they naturally fall into the frequencies where the basic music is less dense.

Sounds interesting, as the recordings that have to be digitalized are fairly complex, a large symphony orchestra plus a large choir. I have been wondering, why some microphones do very, very well on small chamber music settings and fail on large orchestra's, while others do both. Could that be non-linear distortion of the pre-amp, or is that related to distortions in the microphone membrane?

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
The noise and the nonlinearities could add sounds that mask the detail in the signal.

So it comes down to noise for a large part. I will take a look at those sum+difference tones smile.gif

This post has been edited by ktf: Mar 8 2011, 18:06


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Arnold B. Kruege...
post Mar 8 2011, 19:09
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QUOTE (ktf @ Mar 8 2011, 12:02) *
QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
We've all learned that once audio gear meets certain technical standards, it all sounds the same. What has changed over the years is that the cost and size of audio gear that meets certain standards has decreased dramatically.
(...)
Thing is that even inexpensive DACs such as the one in cheap digital music players such as the Sansa Clip, or the motherboard audio interface in your computer, are now really very good. They are capable of sonic transparency, which is the ability to reproduce sound without adding anything that makes it sound different, even in terms of the smallest things that we can reliably hear, or sense in any way.


I really don't understand how that is possible actually: I study mechanical engineering, in which I'm confronted with the aspects of mass-production. The idea is simple: when something costs more at no benefit, don't use it. I guess a motherboard-manufacturer would choose the cheapest audio-gear it can get: most costumers really don't care, they won't complain about sub-par audio. If they complain, it will be about the DAC, not the ADC, as they do not expect much of those cheap built-in microphones.


There is a spectrum of costs from mechanical engineering to electronic engineering to software engineering. At one extreme (mechanical) materials cost and production costs are relatively high. For electronics, particularly microelectronics, the materials and production costs are small and decreasing. For software, materials and production costs are about nil. IP is an increasing portion of the sales costs of all 3. Value is increasingly perceived value as opposed to being inherent in the cost of materials. Modern audio gear is at the intersection of microelectronics and software.

It takes few if any more materials or processing to make a good DAC as opposed to a poor one. The difference is almost all IP and the IP is becoming increasingly well known (and therefore less costly).

The market for DAC chips is very competitive, and if someone can add a zero in front of his chip's THD spec, he's going to win most design competitions. This goes on until there's only one guy selling DACs which seems a long ways away.

QUOTE
Placement of these chips won't get a high priority either, as placing and shielding an audio-chip as it should would cost them several dollars I guess,


The sound chips that they put on motherboards generally get no add on shielding at all. A lot of their noise resistance comes from the fact that they are tiny so they act like poor antennas.

QUOTE
As opposed to what I would expect, computer-audio is certainly not bad, is making audio sound good that easy?


Certainly the vendors are making it look easy. The finesse the board design IP problem by providing "reference designs" of all of the necessary circuit board traces.

QUOTE
I was thinking in a similar way about my Creative X-fi, as it major selling point is surround output, not quality input. Why would they spend a few bucks per unit in getting the ADC right, if (nearly) nobody cares? Why would they meet those minimum quality standards?


Creative got spanked in the market place some years back when they tried to compromise sound quality

QUOTE
.
In 'professional' equipment, things are different. Specs are read, and if the device doesn't meet the expectations, it will be returned, named and shamed. I can understand why equipment made for the job is well built. I wonder with consumer equipment however, as no one seems to care.


Things are evolving predictably. Once quality gets so high that nobody hears any faults that are due to the chips, things will probably level off. In many cases (like the Clip) the DAC becomes part of the same chip that carries the CPU.


QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
For example, if you want people to overlook modest amounts of nonlinear distortion in a demo, you might use recordings of a solo instruments or a certain kind of voice. There won't be a lot of different concurrent tones in the music, and most of the distortion will come out as harmonics which might be overlooked or even preferred. If you want a listening test that is very critical of nonlinear distortion, you might pick a complex sound like a choir. Choirs are particularly good because their signal is dense in the midrange, but leave a lot of less-used frequencies at the extremes. Any sum and different tones that are created will be more audible when they naturally fall into the frequencies where the basic music is less dense.


QUOTE
Sounds interesting, as the recordings that have to be digitalized are fairly complex, a large symphony orchestra plus a large choir. I have been wondering, why some microphones do very, very well on small chamber music settings and fail on large orchestra's, while others do both. Could that be non-linear distortion of the pre-amp, or is that related to distortions in the microphone membrane?


I do a fair amount of recording of bands, orchestras and choirs at State festivals. On site people ask me how I get my recordings to sound so good, so I must be doing something right! ;-)

One setup I use is composed of just a single fairly inexpensive stereo mic, the Rode NT4 (about $400), an inexpensive mic preamp (< $200), and a relatively inexpensive digital recorder. Much of "The trick" is getting the mic in the right place and pointing the right direction. Once I know a room I just walk in, set up, make a few checks and roll. I can often size new rooms up so that I'm close on my first try and can fine tune between the first few groups.

Mics are generally very free of nonlinear distortion because distortion in transducers is dominated by issues related to diaphragm movement and mic diaphragms don't move much. Far more important is frequency response as a function of acceptance angle. Distances from sources and the room boundaries to the mic (and what the room boundaries are) together with mic response versus acceptance angle pretty much control how the recording will sound.

Differences among electronics, particularly nonlinear distortion other than clipping, are decreasing as strong influences in system sound quality.

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ktf
post Mar 8 2011, 21:25
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QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
For electronics, particularly microelectronics, the materials and production costs are small and decreasing.

While small, there is no reason not to use even cheaper components. Quality of audio is generally not a selling point of motherboard or portable audio devices. (just being capable of outputting sound is a selling point) For example, I own a Sansa Fuze, which is perfectly capable of driving my headphone to unhealthy high levels. While I accepted that as normal, I recently borrowed a (there the name is again) Creative Zen in the same price class: it distorted the sound because it was not able to drive the headphone at levels above average. That again contrasts with the theory: why would Sandisk use this probably more expensive DAC that is able to drive higher loads? I don't think of Sandisk of a higher quality brand than Creative regarding audio, I guess the few people pleased by the performance of that Fuze wouldn't compensate for the expenses on the better chips. Probably theory is just theory, and probably some people do care about making quality products, no matter whether it pays back or not. smile.gif

QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
It takes few if any more materials or processing to make a good DAC as opposed to a poor one. The difference is almost all IP and the IP is becoming increasingly well known (and therefore less costly). The market for DAC chips is very competitive, and if someone can add a zero in front of his chip's THD spec, he's going to win most design competitions. This goes on until there's only one guy selling DACs which seems a long ways away.

Then again, a better chip can be sold for a better price. Why would an ordinary manufacturer choose a better, more expensive chip? I presume better is more expensive, as that is just plain logic: if you manufacture something superior in specs to the others, you'll sell it for a better price as one should have more to spare for higher quality. Or am I just wrong? At the other hand indeed, in a competitive market, one wants to gain market share by providing higher quality products in the same price range, but probably also by dumping even cheaper stuff.

QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
The sound chips that they put on motherboards generally get no add on shielding at all. A lot of their noise resistance comes from the fact that they are tiny so they act like poor antennas.

When I plugin my external soundcard, the quality of my internal card drops: it starts to hum. I guess that could be prevented by better shielding or decoupling. Again, that's something manufacturers don't want, as it costs them money and most people do not care.

QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
Creative got spanked in the market place some years back when they tried to compromise sound quality

Definitely good to hear that.

QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
Things are evolving predictably. Once quality gets so high that nobody hears any faults that are due to the chips, things will probably level off. In many cases (like the Clip) the DAC becomes part of the same chip that carries the CPU.

Then again, integrating it, the cost is even more important to the manufacturer producing that CPU, as not every implementation uses this function extensively and this market is probably even more competitive than the DAC-market.

QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:38) *
Much of "The trick" is getting the mic in the right place and pointing the right direction.

Of course, the art of recording itself is the most important. However, we usually use about 8 microphones and pick one or two pairs that sound best. Recordings are so unpredictable that we really can't know which mic to choose beforehand. However, it is surprising that some mics do chamber music (which is not complex) very well, however, when the complexity rises, they miserably fail when compared to the other mics that are just next to it, so it should not depend on the way of recording I guess. I really don't get which specification can describe this ability to resolve complexity.


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Arnold B. Kruege...
post Mar 8 2011, 22:59
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QUOTE (ktf @ Mar 8 2011, 15:25) *
QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
For electronics, particularly microelectronics, the materials and production costs are small and decreasing.

While small, there is no reason not to use even cheaper components. Quality of audio is generally not a selling point of motherboard or portable audio devices. (just being capable of outputting sound is a selling point)

For example, every Asus motherboard I've ever bought bragged about its audio on the outside of its box. Some of their product is obviously being sold to the HTPC market.

QUOTE
For example, I own a Sansa Fuze, which is perfectly capable of driving my headphone to unhealthy high levels. While I accepted that as normal, I recently borrowed a (there the name is again) Creative Zen in the same price class: it distorted the sound because it was not able to drive the headphone at levels above average. That again contrasts with the theory: why would Sandisk use this probably more expensive DAC that is able to drive higher loads?


Sansa may have had much choice about the DAC. Its DAC is on the same Australian Microsystems AS3525 chip along with the CPU and DSP. Please see Rockbox web site Clip+ hardware information

The output voltage of a digital player is set by its headphone amp, not its DAC. The Sansa headphone amp is a very sophisticated design with no oubput coupling capacitors and a very low source impedance. AMS idd a good job on teir AS3525 chip. BTW its CPU can potentially run Windows 7.

The AMS 3525 DAC's specs are:

DAC: 18bit with 94dB SNR (A weighted)
ADC: 14bit with 82dB SNR (A weighted)
Sampling Frequency: 8-48kHz
32 gain steps @ 1.5dB and MUTE

Which it meets or beats according to my measurements and listening tests. Basically it preforms as well if not better than a good stereo receiver being driven by a good CD player.

QUOTE
QUOTE (Arnold B. Krueger @ Mar 8 2011, 19:09) *
The sound chips that they put on motherboards generally get no add on shielding at all. A lot of their noise resistance comes from the fact that they are tiny so they act like poor antennas.


When I plug in my external soundcard, the quality of my internal card drops: it starts to hum. I guess that could be prevented by better shielding or decoupling. Again, that's something manufacturers don't want, as it costs them money and most people do not care.


The hum is no doubt due to a ground loop, and is very likely lowering your estimate of its sound quality. The ground loop is your doing so it is up to you to address it. I'll bet it does not hum when driving just headphones.


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mixminus1
post Mar 8 2011, 23:17
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QUOTE (Arnold B. Krueger @ Mar 8 2011, 13:59) *
I'll bet it does not hum when driving just headphones.

...nor when the laptop's power supply is unplugged and it's just running on its battery - @ktf, try it. smile.gif


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Posts in this topic
- ktf   Quality aspects of ADC   Mar 3 2011, 22:45
- - DVDdoug   The only thing I'd even consider is noise. A...   Mar 3 2011, 23:52
|- - ktf   QUOTE (DVDdoug @ Mar 3 2011, 23:52) The o...   Mar 4 2011, 16:19
- - DonP   One thing that's been an issue in the past is ...   Mar 4 2011, 17:08
- - DVDdoug   QUOTE So, the THD+N (for distortion and non-linear...   Mar 4 2011, 20:51
|- - ktf   QUOTE (DVDdoug @ Mar 4 2011, 20:51) With ...   Mar 4 2011, 23:42
|- - Notat   QUOTE (ktf @ Mar 4 2011, 16:42) It also r...   Apr 5 2011, 15:18
|- - ktf   QUOTE (Notat @ Apr 5 2011, 15:18) Apologi...   Apr 5 2011, 15:23
|- - Notat   In your setup, there are two ground paths between ...   Apr 5 2011, 18:49
|- - Arnold B. Krueger   QUOTE (Notat @ Apr 5 2011, 13:49) In your...   Apr 6 2011, 14:37
- - Arnold B. Krueger   QUOTE (ktf @ Mar 3 2011, 16:45) That frie...   Mar 8 2011, 13:38
|- - ktf   QUOTE (Arnold B. Krueger @ Mar 8 2011, 13...   Mar 8 2011, 18:02
|- - Arnold B. Krueger   QUOTE (ktf @ Mar 8 2011, 12:02) QUOTE (Ar...   Mar 8 2011, 19:09
|- - ktf   QUOTE (Arnold B. Krueger @ Mar 8 2011, 19...   Mar 8 2011, 21:25
||- - Arnold B. Krueger   QUOTE (ktf @ Mar 8 2011, 15:25) QUOTE (Ar...   Mar 8 2011, 22:59
||- - mixminus1   QUOTE (Arnold B. Krueger @ Mar 8 2011, 13...   Mar 8 2011, 23:17
|- - Kees de Visser   QUOTE (Arnold B. Krueger @ Mar 8 2011, 20...   Mar 15 2011, 13:34
|- - Arnold B. Krueger   QUOTE (Kees de Visser @ Mar 15 2011, 08:3...   Mar 24 2011, 12:32
|- - DonP   QUOTE (Arnold B. Krueger @ Mar 24 2011, 06...   Mar 24 2011, 12:53
- - ktf   QUOTE (Arnold B. Krueger @ Mar 8 2011, 22...   Mar 13 2011, 22:49
- - ktf   Today I made some recordings which made me wonder ...   Mar 22 2011, 21:56
|- - Arnold B. Krueger   QUOTE (ktf @ Mar 22 2011, 16:56) I usuall...   Mar 24 2011, 12:51
|- - ktf   Woops, I forgot about this topic. I have set track...   Apr 5 2011, 10:19
- - 2Bdecided   Cleaning and demagnetising the heads, matching the...   Apr 6 2011, 15:14
- - Arnold B. Krueger   QUOTE (ktf @ Mar 3 2011, 17:45) Hi all...   Jun 6 2012, 13:20


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