Shure 55 Audio Processing for SSB - Recommendations?

Discussion in 'Microphones, Speakers & Audio Processing' started by SWL37632, Aug 9, 2021.

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  1. SWL37632

    SWL37632 QRZ Member

    Would like to have recommendations on what kind of audio processing is needed and or desired for a Shure 55 (1940's) microphone for SSB ham use.

    My unit has the selectable low/med/high impedance option.

    I understand that this mic was predominately designed for broadcast music and has a fairly flat frequency response up to about 16-18 KHz.....obviously, ham SSB tops out about 2.5 to about 3 KHz.

    Thanks in advance.


    20+ WPM 1970's Extra
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    No processing is needed.

    Most radios provide very good audio with the matching OEM mics.

    -Many new radios have basic equalizer settings

    -There are zillions (technical term) of audio processors and equalizers available on the market. Pick your level of complexity and features. Hint: "Roger Beeps" and "Echo" are not good choices. :)

    Have fun.

    Here is a good starting point for enhanced ham audio.
    SWL37632 likes this.
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page


    p.s. Don't confuse HiFi or 'Enhanced Audio" with necessarily running wider bandwidth. Two separate things, and one does not require the other.
    SWL37632 likes this.
  4. KF6YIJ

    KF6YIJ Ham Member QRZ Page

    This is correct. Huge difference between 3 khz unprocessed mud, vs 3khz enhanced processing and eq. Wider than that, you enter a niche hobby with only a few hundred enthusiasts. Ultimate test is a buddy receiving you at low volume, if you sound just as good at low volume vs high, you are good to go.
    SWL37632 likes this.
  5. SWL37632

    SWL37632 QRZ Member

    Thanks to all for the info.
  6. WE4E

    WE4E Premium Subscriber QRZ Page

    Needed? None. Desired? Sky's the limit really, although more is rarely better.

    Basics- compression, limiting, eq. Properly adjusted, the radio doesn't have to work so hard to control levels. More consistent ALC, and generally lower so less distortion and other products. Too much compression makes it sound "pumpy" and will raise background noise when you take a breath. Don't go nuts with the EQ either. Frequencies well outside the radio's audio bandpass are wasted energy. You'll want up to about 5khz included because even though the radio can't deal with them, there's information about articulation contained there that's useful. You'll have to experiment on where to cut that off. And don't go nuts with the bass either. Anything much below 150hz is also wasted, generally. You're looking for a balance to make your voice natural and intelligible, and since voices are different, one size does not fit all. If you use headphones, take what you hear with the "monitor" function with a grain of salt. They're usually not a good indication of your transmitted audio. That function is to provide mic sidetone when you're wearing cans, and it doesn't take into consideration head resonances and bone conduction. Have someone you trust with adequate receiver capabilities talk you in.

    There are some already in the ham space - W2IHY (I like the EQ plus, not so much the 8-band), UR6QW makes a nice compressor/eq, and those are intended for radios. There are others.

    In the "pro audio" space, there's literally gobs of stuff. The majority is "line level" and you'll need a mic preamplifier on the front end and a resistive pad on the output to match the level into the radio.

    An easy option is the DBX268s. It has a mic pre in it, and a compressor and downward expander. Stay off the de-esser and enhancer, as those operate on overtones that the radio just can't deal with, and they'll manifest as gross distortion. The downward expander acts like a very gentle squelch that will turn the mic gain down between words so you don't hear background noises. The output will have to be padded down a little. Google "t-pad calculator". I've built many, and with 1/8" resistors, they fit inside XLR and Foster connectors.

    I also like the JoeMeek "Three-Q". It's a mic pre, compressor and eq in one small box, and it has a level switch on the back that can help a lot matching into a radio.

    That's just a couple of a myriad of examples. You don't have to go nuts, you don't have to spend a fortune, and you don't need a four-foot-tall rack of stuff. Whatever it is you choose, if you can keep from turning all the knobs to 11, you'll be ok.

    Don't get hung up on mic impedance. In most cases it doesn't matter. The only time you care is if you try to use a high impedance mic on a low impedance radio input. The radio loads the signal and you can't get enough mic gain, and the audio can be weak and tinny. A low impedance mic will drive a high impedance input all day.

    That's generally true, and for most uses 3khz is more than adequate. With more modern radios, audio bandwith options are more open. Flex and Apache Labs SDRs will let you set it, even up to 20khz. Some Kenwood radios have been able to go over 3khz for ages, and some more modern Yaesu have a magic chant that will give you 4khz. Obviously you have to pick your environment when using those options.
  7. SWL37632

    SWL37632 QRZ Member

    Very educational post. Thank you for sharing.

    I'm still processing the info....

    I did a hook-up test with my primary rig (IC-7000) yesterday with the Shure 55.

    With the rig mic adjustment at 100 %, I have to speak very loudly to get any power out from the rig. Most output occurs with the mic impedance switch at 'medium' impedance.

    Looks like I'll need at least an outboard mic amp for starters.
    KA0HCP likes this.
  8. WE4E

    WE4E Premium Subscriber QRZ Page

    Icom radios traditionally want higher mic inputs, that's not uncommon at all.

    How did you wire it?
  9. SWL37632

    SWL37632 QRZ Member

    From the Shure 55 connector to about 18 inches of microphone 'curly cord' to an 8 conductor connector that fits my IC735.

    When with the 7000, standard 8 conductor adapter (about 5 inches long) to the rectangular plastic connector that fits into the mic input in the back of the 7000.

    The low output is also happening with the 735.

    Conductor wiring is compliant to whatever the 735 needs.... the 'curly cord' was new a dozen years ago when I replaced the original cord.

    I typically use the Icom electret SM20, which includes equalizer, compression, etc, with both rigs with no problems. Take a look at my avatar pict and you can see the SM20 in the lower left hand corner.
  10. WE4E

    WE4E Premium Subscriber QRZ Page

    I was asking about the specific pinout you used.

    Pin 2 on the mic should go to pin 7 on the Icom. Pins 1-3 shorted together go to pin 1 on the Icom.

    There's a wrinkle. There will be 8vdc bias voltage on pin 7 on the Icom, and you'll need a small blocking capacitor to keep that off the mic element. Something like a 1uf or 2.2uf 16v should be adequate. If you use a polarized electrolytic, make the + terminal connection to the radio. Some would advocate a non-polarized electrolytic, but I've never found that necessary in this application. That may be partially responsible for your low mic level, if the diaphragm is pinned to one end by the bias voltage.
    SWL37632 likes this.

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