Hi fidelity SSB bandwith

Discussion in 'Ham Radio Discussions' started by K1VSK, Feb 27, 2007.

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  1. AB0WR

    AB0WR Ham Member QRZ Page

    I have listened to the clip with the HA's in. Neither they or my ears have any problems with anything in the bass range.

    It's just that you don't have a bass voice like Tennessee Ernie Ford. Most people don't, even announcers. You *do* hear that on the ham bands sometimes. I suspect because as someone pointed out (perhaps you) that some mic's will cause that because of their response characteristics.

    tim ab0wr
     
  2. N3JI

    N3JI Ham Member QRZ Page

    I agree with pretty much everything you said here.  I find myself hardly ever cutting the bottom end, other than when the noise & QRM are at extreme levels.  For my operating habits, that seems to be during contests/pileups when I'm *really* trying for some rare station that's down in the dirt.  The preemphasis is definitely very bright, but when the noise levels increase, it sure punches though!  In fact, I'll probably have another look at my "punchy" settings to see if cranking the highs up even more will be of benefit.

    I have a pretty decent receive audio setup in my shack, but most of the time the guys I ragchew with have fairly balanced audio; not too many lows, and just the right amount of highs.  Only occasionally have I heard someone with what I consider "over the top" highs, and that's usually when they're just getting started, changed a lot of things around, got a new mic, etc.  That said, I'm listening to these clips on two different PCs.  I'm using Boston Acoustic speakers with a subwoofer on one and very good headphones on the other.  Similar results with both.

    I'm not sure what the answer to this is.  Since carbon mics were the first ones used I believe, I wonder what their natural frequency response is.  I've never really thought about the initial BW used on AM, but I'm betting it was limited by those old mics.  I could be wrong -- I'm just going on gut feel here...

    Joe, N3JI
     
  3. N3JI

    N3JI Ham Member QRZ Page

    LOL...  Okay, okay...  I know I don't have THIS VOICE.

    But I'm not squeaky, either.

    [​IMG]
     
  4. K7OP

    K7OP XML Subscriber QRZ Page

    Your correct, you DONT get it.  We enjoy sounding how we want to sound. IF your rcvr doesn’t open up to 6khz, and I’m pretty sure it doesn’t, then you cannot hear the fidelity.  My rack may cost more than most HF rigs but to me it's worth it.
    K7OP
     
  5. AB0WR

    AB0WR Ham Member QRZ Page

    Boy, this is a tough one!

    I *like* the sound of the middle clip better even though the noise is higher than on the last clip.

    I'm not sure I can tell any difference in the intelligibility between the middle clip and the last clip, however.

    I *still* can't hear the "d" on inexperienced at this bandwidth while I can on the 7khz clips.

    I suspect the only way to really separate the intelligibility issues is to actually record some test syllables, words, and sentences and then actually play them for test subjects and record the results.

    tim ab0wr
     
  6. K3VR

    K3VR Ham Member QRZ Page

    A little bit about the history of preemphasis in AM radio:

    In the 80's, AM broadcast receivers were being designed with narrower and narrower filters and purposely limited audio response to prevent reception of interference at night as propagation changed. AM broadcasters were upset about this manufacturing trend, because they said it meant people were migrating to the FM band in search of the greater fidelity they were used to.

    In 1986, responding to their concerns, the National Radio Systems Committee (NRSC) proposed a standard AM transmission response with a sharp audio cutoff at just under 10 kHz along with a standard pre-emphasis curve for stations operating in the AM broadcast band.  The standard was designed to allow the manufacturers of radios to increase the bandwidth of receivers for improved audio response while allowing radio stations to standardize bandwidth for acceptable fidelity while lowering the received interference from first adjacent stations in low signal areas.

    "Many receivers using ceramic filters with narrow response characteristics can not be improved by use of excessive preemphasis. These receivers can not hear the transmission of preemphasized high audio frequencies. But excessive preemphasis will foster adjacent channel interference and cause wideband radios to sound shrill or strident." [NRSC-1]

    "Audio response is best measured by detecting the over-the-air signal, This will ensure that the AM transmitter and antenna combination is faithfully reproducing the preemphasized audio." [NRSC-1]

    "Some AM stations with transmitter or antenna problems may not be able to pass preemphasized audio without introducing "splatter" interference and/or overmodulation. If a station transmission system cannot "handle" the NRSC recommended curve, it is suggested that a lower amount of preemphasis be used until the problems are corrected to allow the NRSC curve to be faithfully implemented." [NRSC-1]

    A corresponding deemphasis curve was proposed for the manufacture of AM radio receivers that would match the preemphasis of the AM stations. "...the implementation of preemphasis/deemphasis standards produces transmission/reception system that is essentially flat to nearly 10 kHz  and limited only by the AM  receiver's choice of bandwidth." [NRSC-1]

    "Selectivity and Frequency Response [of Receivers]: Narrowband  50 Hz to 5000 Hz +/-  X dB; Wideband  50 Hz to 10,000 Hz +/-  X dB (Where X is the maximum deviation from the recommended frequency response, and 5000 Hz and 10,000 Hz are example frequency specifications.) The deviation X shall be of as low a value as practical." [NRSC-1]

    NRSC-1 Was adopted by the FCC in 1990. See the NRSC document below for the preemphasis/deemphasis figures in use on the AM Broadcast band.

    NRSC STANDARD
     
  7. K3VR

    K3VR Ham Member QRZ Page

    Hints, Tips, and Recommendations for Amateurs Experimenting With Increased Fidelity/Intelligibility SSB

    1. A receiver section employing a crystal filter system like a Collins KWM-2 will not hear any bandwidth change beyond 2,700 Hz, or below 300 Hz, by virtue of the "brick wall" filtering system. Many radios in use on the amateur bands today will be "deaf" to improvements in audio fidelity and intelligibility due to receiver design parameters.

    2. In contrast to #1, a receiver like that found in an Icom 756 Pro III can detect and appreciate bandwidth changes between 100 Hz and 3,600 Hz. Therefore, improvements in intelligibility and fidelity can be detected out to the maximum receive bandwidth of 3,600 Hz in SSB. Likewise, a Kenwood TS-850 with DSP-100 can detect bandwidth changes resulting in improved intelligibility out to approximately 6 kHz. Many other radios currently in production can also detect increased bandwidths.

    3. An improperly adjusted carrier point in a radio like a Yaesu MkV will cause an increase of transmitted energy on the unwanted sideband, adding nothing to fidelity or intelligibility, but vastly increasing interference potential to other spectrum users.

    4. Too much audio preemphasis may cause IM3 and IM5 products to increase, causing potential for interference. It is the transmitting station's responsibility to monitor IMD carefully.

    5. Receiving stations with noise blankers engaged will often complain of "splatter," when in fact, the noise blanker is adding unwanted artifacts to the recovered audio in the receiver.

    6. Stations operating receivers in close proximity to other stations will often complain of "splatter" when in fact they are simply attempting to operate within the transmitted bandwidth envelope of the other station's transmitter. Let them know your transmitted bandwidth is wider than 3 kHz. Determine whether or not a frequency change is in your best interest.

    7. The goal of achieving fidelity is sometimes at odds with the goal of achieving intelligibility. Because the energy present in the human voice drops off as frequency increases, preemphasis may be required to bring the level of certain consonants to a point where other stations (with appropriate equipment) can hear them with the desired intelligibility. Preemphasis decreases fidelity but it may improve intelligibility, particularly in high noise environments.

    8. High Fidelity audio has traditionally represented a flat audio response, between zero and 20,000 Hz. Audio transmitted in narrower bandwidths may benefit from the use of preemphasis with the goal of improving intelligibility when wider bandwidths are impractical. The benefits of higher fidelity transmissions are only practical when, A.) Space is available for such transmissions without causing interference, and, B.) When atmospheric noise levels are low enough for the receiving station(s) to appreciate increases in fidelity.

    9. Amateur stations employing preemphasis should use sufficient detection methods (oscilloscopes, spectrum analyzers) to be certain their transmitters are not the cause of harmful interference and spurious emissions. [See note] Any kind of audio processing, compression, or equalization scheme, including the predetermined +4dB rise in many microphone elements could conceivably contribute to harmful interference. Ensuring the transmission of a 'clean signal' should be considered a primary part of "good amateur practice."

    10. Any introduction of nonlinearity (overload to the point of distortion) to the transmission system, whether in audio or RF amplification, will potentially result in greater interference potential. Grid driven tubes or improperly filtered 12v transistorized amplifiers, for example, are inherently less linear than amplifiers driven by triodes. The RF output of amplifiers should also be monitored.

    11. Improper tuning of linear amplifiers, overuse of preemphasis, introduction of nonlinear audio, overuse of compression and/or processing, "turning up" the power output of amateur transceivers (creating nonlinearity) in order to provide higher drive for RF amplifiers, and RF feedback (antenna problems) will also present greater interference potential.

    12. Increased low frequency response means that stations who are even 10 Hz "off frequency" from the receiving station will sound unnatural. Stations experimenting with transmitting low frequencies (under 100 Hz) are encouraged to employ transmitters using strict frequency tolerances. A TCXO referenced to WWV is highly recommended.

    The Bottom Line: Major increases in SSB intelligibility and fidelity are possible. The responsibility for interference mitigation and running a clean station rests solidly with the station doing the transmitting. Amateur stations experimenting with higher fidelity/intelligibility must ensure that their transmissions comply with accepted standards of spectral purity.


    [Note] Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products. Make sure your station's transmitted signal complies with FCC rules!

    .
     
  8. N5RFX

    N5RFX Ham Member QRZ Page

    Here are some 1/3 octave band displays for the 3 samples in the pre-emphasis_de-emphasis clip. The 4th display is a reference display that shows the sample as it was downloaded off of the Internet.

    73,

    Mark N5RFX
     
  9. N5RFX

    N5RFX Ham Member QRZ Page

    Here are some 1/3 octave displays of a male voice (Ted Koppel) left, and a female voice (NPR Female voice used in this thread) right. These were taken from the Internet and have not been processed since that time.

    73,

    Mark N5RFX
     
  10. N5RFX

    N5RFX Ham Member QRZ Page

    One last post on this thread. I found a microphone and recorded 3 samples.

    1st 200 - 3000Hz
    2nd 200 - 4500 Hz
    3rd wide open 20 - 16K (mic specs)

    N5RFX audio file
    73,
    Mark N5RFX
     
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