The following information has been culled from:
[email protected]
Paul
Feb 12 #85734
Hi
if any of your tuners have an "FM deviation" meter, you would spot which stations compress and which don't or not as much. Basically if the needle is static regardless of the music playing then they compress. If the needle moves within a range with the music then they compress less and if the music moves freely as the music plays then it is uncompressed.
Using your ears, try to focus on quiet vs loud passages of a given song ; if not much difference or very little difference; then they are compressing.
The trouble now is the actual recordings (regardless if CD or vinyl) have compression to begin with. That's how they were recorded/mastered, then they are played on a radio station that further applies compression so you get a double whammy. But for kids using cheap ear buds or people in their cars it doesn't matter, it actually helps against background noise, but for us dying birds that actual sit and listen in the dark with no book or tablet in our hands, it does create fatigue and disappointment.
Rick Price
Feb 12 #85736
I advocate keeping our terminology and symptomology "grounded" if we can.
Compression in NEW Music CD's/Digital downloads is certainly "a thing" and it's not a good thing. (But then, in my opinion, neither is most of the Music.) By contrast, most newer reissue CD's (of analog recordings from earlier eras) sound much better than their foregoing initial "shove 'em out the door without the benefit of remastering-we got quotas to meet" CDs from the '80s.
There are, as with everything, exceptions.
John Ess
5:45am #85738
No one's actually explaining what compression is here. Basically...and I use that word carefully so as not to get flamed...compression affects the audio signal level in so that there's an overall squeezing of the dynamic range. The loudest portions are lowered in level and the quietest portions are raised in level. This allows the total audio signal to be raised...in some cases too much. The perceived changes make the station sound louder...which with some types of music, and with some ears, becomes more attractive to listeners tuning around. It's easily noticed in tuners that have a deviation meter. With compression, the meter hardly moves because of the loss of dynamic range. Usually any decent stations broadcasting classical music will use very little if any compression, and you'll see it on the meter. College level stations may or may not use it, depending on the sophistication of the equipment they use. That's it in a nutshell.
Joseph Strickland
07:27 #85739
The early units that were produced before the FM MPX method was approved by the FCC had more selective IF transformers and detector transformers (narrower IF bandwidth). They are better able to tune in weak stations next to strong alternate channel stations. Once the FCC approved the GE/Zenith MPX system and manufacturers began to create stereo versions of their FM tuners/receivers they discovered that wider bandwidth was needed in order to decode the stereo signal with good separation and low noise. Many had to add an extra stage of IF amplification/limiting in order to achieve low noise reception of the stereo signal. Wide bandwidth FM detector transformers became necessary and were implemented. The wide bandwidth detectors exhibit the downside of being easier for alternate channel and adjacent channel stations to interfere with the reception of the desired station. The same remained true of the early transistorized FM tuners/receivers until the introduction of elaborate multi-pole IF filters of the LC type were introduced in the late 1960s and early 1970s. Finally ceramic IF filters were introduced which had much better selectivity (provided that they were test selected). Eventually manufacturing processes improved in the ceramic IF filters until not so much test selecting was necessary. Many of our expert members here can test select ceramic IF filters for lowest distortion in the detected signal. Low group delay consistent with good selectivity is the goal because that combination produces the best overall reception.
There are always trade-offs no matter the design. There have been some proposals for improving the FM stereo signal generation and reception. One method suggested changing the MPX analog signal from double-sideband to vestigial sideband in order to reduce the noise present in the demodulated stereo signal. This did help, but the developer could not convince the FM broadcasting and manufacturing community to go along with the recommended changes. It would have caused cost increases for all broadcasters to modify their MPX signal generating equipment along with changes in the manufactured receiving equipment. Then came the IBOC HD digital multiplexing approach for both AM and FM stereo. Those methods are capable of creating CD quality reception (with the caveat of the 15kHz upper frequency limit on FM). A good HD demodulated signal at my house does produce completely noiseless reception as long as the signal is strong enough for the digital decoder to lock onto the digital signal. Once the signal gets weak enough that the digital IBOC decoder does not lock the receiver drops back to analog reception and decoding of the stereo with a dramatic increase in noise.
Another issue with IBOC transmissions is that the received signal on an analog FM MPX decoder equipped receiver/tuner can have interference from the IBOC digital signal show up in the audio. Manufacturers of the better tuners added extra filtering in their MPX signal decoding to help suppress this extra source of noise (in their analog MPX decoding units).
The presence of over-compressed audio being fed into FM transmitters also contributes interference with the reception of weak stations next to strong alternate or adjacent FM station. Welcome to the real world!
[email protected]
Paul
Feb 12 #85734
Hi
if any of your tuners have an "FM deviation" meter, you would spot which stations compress and which don't or not as much. Basically if the needle is static regardless of the music playing then they compress. If the needle moves within a range with the music then they compress less and if the music moves freely as the music plays then it is uncompressed.
Using your ears, try to focus on quiet vs loud passages of a given song ; if not much difference or very little difference; then they are compressing.
The trouble now is the actual recordings (regardless if CD or vinyl) have compression to begin with. That's how they were recorded/mastered, then they are played on a radio station that further applies compression so you get a double whammy. But for kids using cheap ear buds or people in their cars it doesn't matter, it actually helps against background noise, but for us dying birds that actual sit and listen in the dark with no book or tablet in our hands, it does create fatigue and disappointment.
Rick Price
Feb 12 #85736
I advocate keeping our terminology and symptomology "grounded" if we can.
Compression in NEW Music CD's/Digital downloads is certainly "a thing" and it's not a good thing. (But then, in my opinion, neither is most of the Music.) By contrast, most newer reissue CD's (of analog recordings from earlier eras) sound much better than their foregoing initial "shove 'em out the door without the benefit of remastering-we got quotas to meet" CDs from the '80s.
There are, as with everything, exceptions.
John Ess
5:45am #85738
No one's actually explaining what compression is here. Basically...and I use that word carefully so as not to get flamed...compression affects the audio signal level in so that there's an overall squeezing of the dynamic range. The loudest portions are lowered in level and the quietest portions are raised in level. This allows the total audio signal to be raised...in some cases too much. The perceived changes make the station sound louder...which with some types of music, and with some ears, becomes more attractive to listeners tuning around. It's easily noticed in tuners that have a deviation meter. With compression, the meter hardly moves because of the loss of dynamic range. Usually any decent stations broadcasting classical music will use very little if any compression, and you'll see it on the meter. College level stations may or may not use it, depending on the sophistication of the equipment they use. That's it in a nutshell.
07:27 #85739
The early units that were produced before the FM MPX method was approved by the FCC had more selective IF transformers and detector transformers (narrower IF bandwidth). They are better able to tune in weak stations next to strong alternate channel stations. Once the FCC approved the GE/Zenith MPX system and manufacturers began to create stereo versions of their FM tuners/receivers they discovered that wider bandwidth was needed in order to decode the stereo signal with good separation and low noise. Many had to add an extra stage of IF amplification/limiting in order to achieve low noise reception of the stereo signal. Wide bandwidth FM detector transformers became necessary and were implemented. The wide bandwidth detectors exhibit the downside of being easier for alternate channel and adjacent channel stations to interfere with the reception of the desired station. The same remained true of the early transistorized FM tuners/receivers until the introduction of elaborate multi-pole IF filters of the LC type were introduced in the late 1960s and early 1970s. Finally ceramic IF filters were introduced which had much better selectivity (provided that they were test selected). Eventually manufacturing processes improved in the ceramic IF filters until not so much test selecting was necessary. Many of our expert members here can test select ceramic IF filters for lowest distortion in the detected signal. Low group delay consistent with good selectivity is the goal because that combination produces the best overall reception.
There are always trade-offs no matter the design. There have been some proposals for improving the FM stereo signal generation and reception. One method suggested changing the MPX analog signal from double-sideband to vestigial sideband in order to reduce the noise present in the demodulated stereo signal. This did help, but the developer could not convince the FM broadcasting and manufacturing community to go along with the recommended changes. It would have caused cost increases for all broadcasters to modify their MPX signal generating equipment along with changes in the manufactured receiving equipment. Then came the IBOC HD digital multiplexing approach for both AM and FM stereo. Those methods are capable of creating CD quality reception (with the caveat of the 15kHz upper frequency limit on FM). A good HD demodulated signal at my house does produce completely noiseless reception as long as the signal is strong enough for the digital decoder to lock onto the digital signal. Once the signal gets weak enough that the digital IBOC decoder does not lock the receiver drops back to analog reception and decoding of the stereo with a dramatic increase in noise.
Another issue with IBOC transmissions is that the received signal on an analog FM MPX decoder equipped receiver/tuner can have interference from the IBOC digital signal show up in the audio. Manufacturers of the better tuners added extra filtering in their MPX signal decoding to help suppress this extra source of noise (in their analog MPX decoding units).
The presence of over-compressed audio being fed into FM transmitters also contributes interference with the reception of weak stations next to strong alternate or adjacent FM station. Welcome to the real world!
