Disappearing Surround Sound

[Roc Rinaldi]

Who knows the answer to this?

When I play CDs on my system some CDs have songs that play through all 7 speakers. Other songs on the same CD only play through the front L&R and the center speaker. This seems to be happening with older music. Why is this?

[Roc Rinaldi]

Someone must know the answer to this.

[IndyKlipschFan]

Could it be your signal is not strong enough? Your pre amp or cd player re sets in CD mode to stereo, if you using a cd/dvd player?

Or if really old cd's, were they in mono too? hahahaha Sorry, I know too easy...

Make sure all your interconnects are fully pushed in as well.

[Roc Rinaldi]

Yes some are mono songs but my McIntosh MX120 processor says that it can take mono or stereo and put sound into all seven channels which it does on other songs on the same CDs so I don't understand. Some of the stereo songs have sound in all 7 speakers and some only in the 3 front ones. (L+R+C)

?????

[dtel's wife]

I am not real intelligent with some of the audio stuff....how can a processor take something in "mono" and put it through all seven channels? I would think it is directly related to the recording on the CD???? Again, I have no clue...but I would really like to know.

[sfogg]

What mode are you listening in? If it is something like PLII or PLIIx the differences all have to do with the recordings themselves.

The simplified answer... anything in phase and even amplitude between L/R (mono) gets steered to the center channel. Anything 180 degrees out of phase between L/R gets steered to surround.

If the recoring has no out of phase material nothing goes to surround. If it is a mono recording everything goes to center.

Shawn

[Arky]

Your system is possessed.[H]

[IndyKlipschFan]

Roc... Send that McIntosh over here right away,,,, I will be happy to see if it does it to me too? hahahahhaha

I would still look at your cd/ dvd player to see if it is over riding the signal to your pre amp.

[Jay481985]

I am not real intelligent with some of the audio stuff....how can a processor take something in "mono" and put it through all seven channels? I would think it is directly related to the recording on the CD???? Again, I have no clue...but I would really like to know.

mono X7 or stereo X7 basically it takes the signal and splits it however many ways, not true surround sound but ok

[Roc Rinaldi]

I am not real intelligent.

OK.

[Roc Rinaldi]

I am not real intelligent with some of the audio stuff....how can a processor take something in "mono" and put it through all seven channels? I would think it is directly related to the recording on the CD???? Again, I have no clue...but I would really like to know.

It takes mono and stereo and 5 channel signals and simulates signals for the remainder of the seven channels.

[Roc Rinaldi]

What mode are you listening in? If it is something like PLII or PLIIx the differences all have to do with the recordings themselves.

The simplified answer... anything in phase and even amplitude between L/R (mono) gets steered to the center channel. Anything 180 degrees out of phase between L/R gets steered to surround.

If the recoring has no out of phase material nothing goes to surround. If it is a mono recording everything goes to center.

Shawn

Shawn, this sounds like it could be a part of the answer.

[Roc Rinaldi]

Your system is possessed.[H]

For Sale: One possessed system.

[Roc Rinaldi]

Roc... Send that McIntosh over here right away,,,, I will be happy to see if it does it to me too? hahahahhaha

I would still look at your cd/ dvd player to see if it is over riding the signal to your pre amp.

You mean that I can just look at it and tell?

[Arky]

No! You have to ask it nicely.

[Roc Rinaldi]

Aha.

[WMcD]

I sure SFogg is correct.

Remember when Dolby multichannel first came out on VHS? There were still only two soundtracks on the tape. A simple adding decoding circuit put the Left plus Right to the center, just like PWKs mixing box. Also, these voltages add up a bit to make a stronger center image.

The Left right Right went to the surrounds, with a 10 mS delay in the simple decoder. The delay helped the ear detect the surrounds and not the same as the front. Even though it drove two surround speakers, it was simply mono.

= = =

Later, steering circuits were used which helped pick out what was to be sent where.

= = =

Basically, we have to (1) look at signals which show up (ENCODED) as L plus R in the mix and signals which show up as L minus R in the mix or soundtrack. They can be like those because of a deliberate mix or by "accident".

And we have to look at the DECODING (2) which mixes again in a receiver.

= = =

You have to take a closer look at a sound, like chirping birds in a soundtrack, meant to go to the surround or ambiance. It is originally mono, but mixed or encoded to be L minus R on the soundtrack or 180 degrees out of phase in the two tracks (same thing).

In the L + R (left plus right) mix, the encoded L - R doesn't show up at all in the center speaker. This is because the L - R cancel out when added in decoding. That is to say, they actually cancel out as far the center channel decode is concerned.

But it (chirpping birds, mono) is also sent to the surround L - R decode circuit (left minus right). Actually everything (save for steering circuit effect) is sent to the decoder. Remember from high school that a minus times a minus is a plus. Now the encoded L - R signal is output as an additive or L + R. The high school math predicts the flip of - to +.

Therefore it is like having a strong center in the rear. But we send it to two rear speakers. Or more if you have more.

= = =

Old recordings were not set up with such encoding and decoding in mind. However, it sometimes works out like that. Hence "accidental" encoding in an old recording which just happens to work with any decoding system we use..

For example, in some recordings a center performer is exactly in phase (a L + R) in a two channel recording and thus shows up in the center channel with PWK's box. But this varies, which is why people who have tried the mixing box report that the gain for the center channel has to be adjusted. Note that PWK found that 6 dB loss was necessary to get the center level correct, as an average.

Surround or ambiance sound in a two channel recording (IF IT IS THERE - your question) tends to be random in phase because of the echos and path length difference. So it is not giving a strong center. But it can be detected in the surround channel even if it is not exactly L - R.

= = =

People should ask: If the ambiance is random phase in an accidental encoding, doesn't it still show up in the center to some extent? The answer is yes. It does without steering circuits.

Even if we don't have steering, there is still an effect of in-phase versus random phase. Power is a function of any adding voltage being squared. Essentially, this means that ambiance random phase (which adds less) is weaker than in-phase (which does add). (I know this is getting way OT.)

Gil

[Roc Rinaldi]

I sure SFogg is correct.

Remember when Dolby multichannel first came out on VHS? There were still only two soundtracks on the tape. A simple adding decoding circuit put the Left plus Right to the center, just like PWKs mixing box. Also, these voltages add up a bit to make a stronger center image.

The Left right Right went to the surrounds, with a 10 mS delay in the simple decoder. The delay helped the ear detect the surrounds and not the same as the front. Even though it drove two surround speakers, it was simply mono.

= = =

Later, steering circuits were used which helped pick out what was to be sent where.

= = =

Basically, we have to (1) look at signals which show up (ENCODED) as L plus R in the mix and signals which show up as L minus R in the mix or soundtrack. They can be like those because of a deliberate mix or by "accident".

And we have to look at the DECODING (2) which mixes again in a receiver.

= = =

You have to take a closer look at a sound, like chirping birds in a soundtrack, meant to go to the surround or ambiance. It is originally mono, but mixed or encoded to be L minus R on the soundtrack or 180 degrees out of phase in the two tracks (same thing).

In the L + R (left plus right) mix, the encoded L - R doesn't show up at all in the center speaker. This is because the L - R cancel out when added in decoding. That is to say, they actually cancel out as far the center channel decode is concerned.

But it (chirpping birds, mono) is also sent to the surround L - R decode circuit (left minus right). Actually everything (save for steering circuit effect) is sent to the decoder. Remember from high school that a minus times a minus is a plus. Now the encoded L - R signal is output as an additive or L + R. The high school math predicts the flip of - to +.

Therefore it is like having a strong center in the rear. But we send it to two rear speakers. Or more if you have more.

= = =

Old recordings were not set up with such encoding and decoding in mind. However, it sometimes works out like that. Hence "accidental" encoding in an old recording which just happens to work with any decoding system we use..

For example, in some recordings a center performer is exactly in phase (a L + R) in a two channel recording and thus shows up in the center channel with PWK's box. But this varies, which is why people who have tried the mixing box report that the gain for the center channel has to be adjusted. Note that PWK found that 6 dB loss was necessary to get the center level correct, as an average.

Surround or ambiance sound in a two channel recording (IF IT IS THERE - your question) tends to be random in phase because of the echos and path length difference. So it is not giving a strong center. But it can be detected in the surround channel even if it is not exactly L - R.

= = =

People should ask: If the ambiance is random phase in an accidental encoding, doesn't it still show up in the center to some extent? The answer is yes. It does without steering circuits.

Even if we don't have steering, there is still an effect of in-phase versus random phase. Power is a function of any adding voltage being squared. Essentially, this means that ambiance random phase (which adds less) is weaker than in-phase (which does add). (I know this is getting way OT.)

Gil

Gil, Gil, Gil....................I now have a major major headache.

However, I do want to thank you because what you say actually does make sense.

I now need to go and consume about 5 Aspirin and maybe a Bromo.

Thanks again pal.

[IndyKlipschFan]

IndyKlipschFan:

Roc... Send that McIntosh over here right away,,,, I will be happy to see if it does it to me too? hahahahhaha

I would still look at your cd/ dvd player to see if it is over riding the signal to your pre amp.

You mean that I can just look at it and tell?

---

Sincerely,

Roc

============

Yes, doesn't your display on your cd player tell you what signal and what spearkers it is sending the info too? Mine does.

[Roc Rinaldi]

IndyKlipschFan:

Roc... Send that McIntosh over here right away,,,, I will be happy to see if it does it to me too? hahahahhaha

I would still look at your cd/ dvd player to see if it is over riding the signal to your pre amp.

You mean that I can just look at it and tell?

---

Sincerely,

Roc

============

Yes, doesn't your display on your cd player tell you what signal and what spearkers it is sending the info too? Mine does.

Right......and it don't rain in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Indianapolis in the summertime.