IanHarvy asked (more or less, I’m paraphrasing here) whether amplifier distortion shouldn’t always show up on continuous single tone distortion testing and if I could give an example where distortion "hides" from the single tone test
The circuit below gives ~ -90 dB 2nd harmonic distortion at V(out) when probed with a single tone sine but as can be seen, the 2nd order difference freq distortion products are at ~ -9 dB each for the 10+20KHz with the worst case two tone excitation frequencies
You might object that multipliers aren’t common audio amplifier subcircuits until someone points out the near identity of the diff input stage+tail current source and the Gilbert cell multiplier
I think the point of the example is that low single tone THD doesn’t guarantee well-behaved IMD
The circuit below gives ~ -90 dB 2nd harmonic distortion at V(out) when probed with a single tone sine but as can be seen, the 2nd order difference freq distortion products are at ~ -9 dB each for the 10+20KHz with the worst case two tone excitation frequencies
You might object that multipliers aren’t common audio amplifier subcircuits until someone points out the near identity of the diff input stage+tail current source and the Gilbert cell multiplier
I think the point of the example is that low single tone THD doesn’t guarantee well-behaved IMD
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It's a little long winded but there is a point in here somewhere.
Various kinds of instruments sound different because they have different harmonics as part of their accoustical output. Violins and trumpets making the same note sound quite different they both have fairly large amounts of harmonic distortion, but both sound good in the audiophile sense.
As far as I know, accoustical instruments can not create intermodulation distortion products because there aren't any non-linear elements - only electronic amplifiers can have this illness.
This may speak to why a group heard live, even if it is a group with electronic amplifiers, speakers, etc. usually sounds quite distinctively "live" as compared to a recording of the same event.
I have long suspected that this is because most groups play with each musician having their own amplifier and speaker thereby preventing the intermodulation products. I am guessing that these products are one of the recording anomalies that typically allow us to easily distinguish between live and recorded sounds.
Over the years I have read various reviews with hidden speakers and musicians where the listener couldn't tell the difference between a recording and a live source. All of these I can recall used a single instrument at a time for the demonstration.
If I am right, testing with multiple signals and measuring the intermodulation products is an important way to evaluate electronic designs. Not to be taken to mean that listening tests aren't the most important of all.
Various kinds of instruments sound different because they have different harmonics as part of their accoustical output. Violins and trumpets making the same note sound quite different they both have fairly large amounts of harmonic distortion, but both sound good in the audiophile sense.
As far as I know, accoustical instruments can not create intermodulation distortion products because there aren't any non-linear elements - only electronic amplifiers can have this illness.
This may speak to why a group heard live, even if it is a group with electronic amplifiers, speakers, etc. usually sounds quite distinctively "live" as compared to a recording of the same event.
I have long suspected that this is because most groups play with each musician having their own amplifier and speaker thereby preventing the intermodulation products. I am guessing that these products are one of the recording anomalies that typically allow us to easily distinguish between live and recorded sounds.
Over the years I have read various reviews with hidden speakers and musicians where the listener couldn't tell the difference between a recording and a live source. All of these I can recall used a single instrument at a time for the demonstration.
If I am right, testing with multiple signals and measuring the intermodulation products is an important way to evaluate electronic designs. Not to be taken to mean that listening tests aren't the most important of all.
This may be not significant and surely is not a techicaly minded thing. But my dad was listening to my speakers because i'd changed them to open baffle and I wanted to hear his thoughts on it.
He said (not in comparison to the other speakers) but when a single intrument played, it was placed very well in the sound stage and probably sounded more reaslistic. However when the whole band came in that same feel was lost slightly, even thought it still all sounded very good and there was an impressive spread of sound.
He said (not in comparison to the other speakers) but when a single intrument played, it was placed very well in the sound stage and probably sounded more reaslistic. However when the whole band came in that same feel was lost slightly, even thought it still all sounded very good and there was an impressive spread of sound.
Obviously you are correct. Five seconds of discussion with a friend reminded me that there is a reason we make trumpets out of brass instead of lead and violins out of hardwood instead of leather. The overtones created by these materials that flex as sound is made create the character and interest for the instrument. Duh.
That goes to show what single issue thinking and myopia can do. In my own defense, I was focused on the model of feeding accoustic energy into an infintely rigid cavity where I think my hypotesis is correct. No matter how complex the shape, certain harmonics may be emphasized or reduced but no mixing or products will be created.
The other problem may have to do with language. Clipping a sinewave to make it a square wave adds a lot of distortion products. Alternatively, if we feed a square wave to a narrow filter it comes out as a sine wave, is this called distorion?
If certain harmonics are intentionally emphasized in an instrument is that distortion? Reeds and bowed strings produce waveforms with a predictable series of harmonics. Shaping the accoustic path can intentionally enhance some and reduce others, distortion? SET amplifiers have high amounts of even order distortion products, most of us think that sounds good, so we think they sound good. So the origional question, is intentional harmonic enhancement distortion?
My original post was meant along a related line: The debate that intrigues me is "why does electronic reproduction tend to fall quite short of a live event"?
Smarter people than me have worked on this and some things that might seem to be the answer have been mostly ruled out.
Dynamic range? More powerful amplifiers/systems do not automatically sound more life like.
Distortion? There was a period when amplifiers could be bought that had distorion products that were tiny and almost unmeasurable, most sounded perfectly awful.
Frequency response? Again largely ruled out.
I do not know. The debate is confused by accurate vs pleasant. I spend more time on my system reducing "listener fatige" than striving for accuracy but it is often that an improvment in one will cause an improvement in the other. Unfortunately this does not seem hold true every time. Whee.
That goes to show what single issue thinking and myopia can do. In my own defense, I was focused on the model of feeding accoustic energy into an infintely rigid cavity where I think my hypotesis is correct. No matter how complex the shape, certain harmonics may be emphasized or reduced but no mixing or products will be created.
The other problem may have to do with language. Clipping a sinewave to make it a square wave adds a lot of distortion products. Alternatively, if we feed a square wave to a narrow filter it comes out as a sine wave, is this called distorion?
If certain harmonics are intentionally emphasized in an instrument is that distortion? Reeds and bowed strings produce waveforms with a predictable series of harmonics. Shaping the accoustic path can intentionally enhance some and reduce others, distortion? SET amplifiers have high amounts of even order distortion products, most of us think that sounds good, so we think they sound good. So the origional question, is intentional harmonic enhancement distortion?
My original post was meant along a related line: The debate that intrigues me is "why does electronic reproduction tend to fall quite short of a live event"?
Smarter people than me have worked on this and some things that might seem to be the answer have been mostly ruled out.
Dynamic range? More powerful amplifiers/systems do not automatically sound more life like.
Distortion? There was a period when amplifiers could be bought that had distorion products that were tiny and almost unmeasurable, most sounded perfectly awful.
Frequency response? Again largely ruled out.
I do not know. The debate is confused by accurate vs pleasant. I spend more time on my system reducing "listener fatige" than striving for accuracy but it is often that an improvment in one will cause an improvement in the other. Unfortunately this does not seem hold true every time. Whee.
Both you and Mr Fitzpatrick felt that distortion is not the cause of reproduced music sounding unlike live. Neither of you offered alternative opinions, at least not in this thread, that the rest of us could support or not.
This could be a good forum thread topic. As far as I know no real agreement exists on this, yet it is near and dear to the heart of almost any audiophile. (I am new, maybe you've been there and I missed it)
I have spent considerable money on my system and it does seem that for the most part, increased cost relates quite strongly to increased sound quality. I have listened to systems whose prices approached astronomical and while they often sounded quite extraordinarily good they did not sound live.
Perhaps we might start with a multiple choice list where members could weigh their opinion as to the relative influence each item has on this lack. I do understand that every item on the list contributes it's own problems but I have heard recordings where extraordinary efforts were made to minimize problems caused by various pieces of the process
1. Is it the microphone process?
2. The studio environment?
3. The mixing process?
4. The mechanism of recording?
5. The process of decoding (including phono cartridges)?
6. The amplification chain?
7. The speakers?
8. The number of channels?
I've probably missed some and the permutations are huge so a simple answer may well be impossible.
This could be a good forum thread topic. As far as I know no real agreement exists on this, yet it is near and dear to the heart of almost any audiophile. (I am new, maybe you've been there and I missed it)
I have spent considerable money on my system and it does seem that for the most part, increased cost relates quite strongly to increased sound quality. I have listened to systems whose prices approached astronomical and while they often sounded quite extraordinarily good they did not sound live.
Perhaps we might start with a multiple choice list where members could weigh their opinion as to the relative influence each item has on this lack. I do understand that every item on the list contributes it's own problems but I have heard recordings where extraordinary efforts were made to minimize problems caused by various pieces of the process
1. Is it the microphone process?
2. The studio environment?
3. The mixing process?
4. The mechanism of recording?
5. The process of decoding (including phono cartridges)?
6. The amplification chain?
7. The speakers?
8. The number of channels?
I've probably missed some and the permutations are huge so a simple answer may well be impossible.
One starts with the observation that the three-dimensional soundfield present at the time of the original performance (and here I restrict myself to "real" musical events) is not reproduced around the listener's head. Not even vaguely.
So, the primary contributors to this are:
1. The paradigm of two channels. Or even five. Whatever mapping you choose will be inherently inaccurate.
2. The process of properly sampling the original soundfield by microphones. (I use the word "sampling" in the analog sense)
3. The interaction of whatever channel mapping and sampling method one chooses with the listening room.
The simple matter of storing, retrieving, and replicating an analog electrical signal is pretty trivial in comparison.
So, the primary contributors to this are:
1. The paradigm of two channels. Or even five. Whatever mapping you choose will be inherently inaccurate.
2. The process of properly sampling the original soundfield by microphones. (I use the word "sampling" in the analog sense)
3. The interaction of whatever channel mapping and sampling method one chooses with the listening room.
The simple matter of storing, retrieving, and replicating an analog electrical signal is pretty trivial in comparison.
I have listened to "Bi-aural" recordings; they were quite the vogue sometime back. In this process an artificial human head with microphones embedded in the ears is placed in a suitable audience position.
The resulting two-channel signal is recorded and meant specifically to be played back over headphones. The three dimensionality of the experience is quite remarkable, but live? No. In this case all the information that our two channel ears can process is duplicated in a reasonable fashion but the result is not the pinnacle of sound reproduction. So mapping of and by itself does not seem to hold a real answer.
I am certainly no recording engineer but my amateur attempts demonstrate that ears and microphones do seem to work quite differently. So this could be a clue. On the other side, I agree with a stereophile article that said live performances by electronic groups do not sound live when the recordings, presumably taken from the electrical signals rather than the acoustic ones, are played back.
In my first post I refer to articles I have read where people have been unable to differentiate live from recorded. Again all of these I can recall used one instrument at a time. Implying that the microphone, electronics and speakers could effectively fake it under the right conditions. It is this information about possible interactions in the signal path that causes me to be less cavalier about the electronics than you.
Different equipment manufactured by reputable companies can and often does sound distinctively different. The technology is such that a reasonably competent engineer shoudn't have much trouble making a design that achieves repeatable performance, yet many sound different.
This has created an entire industry of reviewers. I rarely agree with all of them and sometimes their credentials are suspect but there is little question that there is something to this. This argues that the electronics certainly seem to contribute to the end result in a significant way.
The resulting two-channel signal is recorded and meant specifically to be played back over headphones. The three dimensionality of the experience is quite remarkable, but live? No. In this case all the information that our two channel ears can process is duplicated in a reasonable fashion but the result is not the pinnacle of sound reproduction. So mapping of and by itself does not seem to hold a real answer.
I am certainly no recording engineer but my amateur attempts demonstrate that ears and microphones do seem to work quite differently. So this could be a clue. On the other side, I agree with a stereophile article that said live performances by electronic groups do not sound live when the recordings, presumably taken from the electrical signals rather than the acoustic ones, are played back.
In my first post I refer to articles I have read where people have been unable to differentiate live from recorded. Again all of these I can recall used one instrument at a time. Implying that the microphone, electronics and speakers could effectively fake it under the right conditions. It is this information about possible interactions in the signal path that causes me to be less cavalier about the electronics than you.
Different equipment manufactured by reputable companies can and often does sound distinctively different. The technology is such that a reasonably competent engineer shoudn't have much trouble making a design that achieves repeatable performance, yet many sound different.
This has created an entire industry of reviewers. I rarely agree with all of them and sometimes their credentials are suspect but there is little question that there is something to this. This argues that the electronics certainly seem to contribute to the end result in a significant way.
Reproducing live sound
A few years ago, there was the sound of a band playing live on the TV. I turned to look, because the music was good and sounded like a jam. On the TV there was a band playing in a living - room, and it sounded like it. Bear in mind that this is mono, through a 3" speaker typical of those fitted to 12" portable TVs.
This demonstrated to me that sounding live has nothing to do with creating a 3d soundstage with expensive equipment.
In a live event, the acoustic cues provided by the venue can be heard, even in mono, and your hearing recognises the pattern of the soundfield.
When listening to something, this soundfield is either there or it isn't, so it sounds live or it doesn't.
A few years ago, there was the sound of a band playing live on the TV. I turned to look, because the music was good and sounded like a jam. On the TV there was a band playing in a living - room, and it sounded like it. Bear in mind that this is mono, through a 3" speaker typical of those fitted to 12" portable TVs.
This demonstrated to me that sounding live has nothing to do with creating a 3d soundstage with expensive equipment.
In a live event, the acoustic cues provided by the venue can be heard, even in mono, and your hearing recognises the pattern of the soundfield.
When listening to something, this soundfield is either there or it isn't, so it sounds live or it doesn't.
IMD will muddy up the reproduced sound by generating signals that simply weren't there before (in both the frequency- and time- domain) and therefore not only blurrying the sound of the instruments but also spatial reproduction.
Low THD is a prerequisite but not a guarantee for low IMD.
Regards
Charles
Low THD is a prerequisite but not a guarantee for low IMD.
Regards
Charles
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