I have now spent a bit
of time
experimenting with transmit audio from the SDR. In the first instance I
purchased a stock Yaesu fist mic that plugged straight in to the front
SDR panel and provided me ptt control. A mic lead ran from the back of
the SDR and then into input 1 of the Edirol. Initial reports on my
audio suggested that I had a very slight echo on my signal - it wasn't
unpleasant to the listener - but was noticeable. In speaking to various
people already using the SDR, it was suggested that this echo would be
eliminated by having a mic plugged directly into the Edirol rather than
going via the SDR. This would also involve me hooking up a separate ptt
line to the radio unless I wanted to use VOX or the mouse to key the
radio. At the same time I was receiving information that people using
the Behringer B-1 mic along with the Behringer 802 mixer were getting
good audio reports. After shopping around I found that the same
supplier of the Edirol FA-66 offered these other products at very
competitive pricing and the mic compared very favorably in comparison
to the Heil line up. Christmas arrived and a B-1 and 802 arrived....
However by October 2007, I found that despite constant tweaking, the
B-1 condenser microphone could not be adjusted to give me a consistently
good audio report. Too much background noise and sensitivity. I emailed
Heil directly and received a reply from Bob Heil who suggested the PR-781. Part of Bob's reply read:
"Condenser microphones are just a tragedy. Yes....a tragedy ! They should NEVER be used in ANY amateur radio, live stage or broadcast application. They have WAY too much gain and cause so many problems in each situation. Phase cancellation between the unwanted sounds they hear and the direct sound you are TRYING to hear gives every one of them a 'strange' sound. Just too sensitive. Condenser mics were developed to record a quiet oboe or violins in the corner of a VERY controlled recording studio. Placing them outside of this venue brings on nothing short of disasters. Too much gain. They pick up everything for 50 feet (or more) and with amateur radio, they are just simply horrible. WAY too much gain and you have to contend with that ridiculous phantom power for the electronics inside which ends up as an 'antenna' causing excessive RFI problems."
Pretty strong stuff! You can read the full email by clicking here.
The PR-781
has XLR inputs, so it was very easy to remove the B-1 and swap them
straight over. As the PR-781 is a dynamic microphone the 48V phantom
supply voltage is not required. I haven't given up on the B1 mic and am
still playing with my settings. See below for a sample audio recording.
I initially borrowed a Heil boom to mount the mic. (There appears to be nothing else on the market like the Heil product - and it is very good.) I had previously made a ptt cable connected to the front of the SDR mic input. My transmit audio flows from the PR-781 positioned by the Heil boom, into the 802 mixer and in turn feeding into the FA-66, ptt controlled by my hand made control cable.
The PR-781 in the operating position.
The Behringer B1 microphone in its' operating position.
The PTT device I made showing the push-button switch at the top, and two inputs for rig cables.
'Audio quality is in the ear of the listener' Below are some
pictures showing the SDR settings.
This image shows the GUI of the SDR. For those familiar with the software, you can see the on buttons showing yellow, Spur Reduction on, Mic Gain at 15, Compression off, CPDR on at 3, RX off & TX EQ enabled and 2.9K receive filter. (As a footnote to this image, you can see the nice clean signal being transmitted at around 14.192MHz, in comparison to the splatter being caused by the station transmitting at 14.220MHz)
This image shows the current EQ settings that I have tailored for my voice. I found that the 3 band EQ easier to use than the 10 band. Notice I have a little bit of transmit pre-amp enabled - this seems to 'boost' the audio without increasing the ALC. Why the effort? Well if you have a look at the image below, you will see that after some EQ, my signal is more flat letting me achieve a better audio spectrum across the bandwidth I am using. This is particularly important for a good SSB signal. I could do some more work with the audio to achieve an even flat-er signal.....
To achieve the following graphs, I used
HamAlyzer software - which is available over the internet at US$30.00 -
there are lots more expensive programs available - but this one works
for me. To run the software I set the SDR with VAC enabled, and I used the virtual cable to
feed the HamAlyzer input.
This image shows the SDR
with no EQ - you can see the base in my audio signal - which in reality
sounds deep and 'muffled'. The following images all have a bit of
EQ'ing using both the Behringer & FlexRadio software.
This image shows the general audio spectrum I am using for normal voice communications. You can see the obvious difference with the audio much flatter and just tapering down from low to high. This setting seems to give generally good reports.
This image shows my setting when chasing DX and using a smaller audio bandwidth. Again the audio is nice and flat.
This image shows the comparison between normal and dx modes. You can see the base and top which takes away the tin type sound of dx transmission.
Just for something different here is an audio graph with my
radio set to transmit with a 4KHz audio bandwidth - ESSB?, I don't use
this mode, but thought I would have a look at what could be achieved. I
think for this type of audio I would need to spend some time
'tweaking'..
This image shows the comparison between ESSB type audio and DX
type audio - you can see that in crowded band conditions there would be
problems with ESSB.
**November 2007** Here is a recording
of some of the audio adjustments I have found using the FlexRadio
software. I am using the Behringer B1 mic and the Behringer 802 mixer.
The mp3 file is 337Kb in size.
Here is another mp3 audio recording made
of my transmitted signal using a transmit 3KHz bandwidth received by
Peter - SM5HUA on 14.178MHz on 19/11/2007. The mp3 file is 421Kb in
size. Peter is a member of the voodoo essb audio crew and is using the
renowned TS950SDX, Peter's web site is well worth a look to get more information on ESSB audio settings and equipment!
As a general disclaimer, I
am not involved with ESSB - so apologies if I haven't described ESSB in
context per above information. I am also aware that received
audio is not always the same between two stations - depending on
equipment, band filter settings, DSP, signal strength, etc etc.
Therefore the best gauge when establishing your own settings is to use
the monitor function on the SDR, and / or a separate radio in your shack and
software such as what is shown above. I discovered a really good web
site
by W3OZ that simplifies the explanation why it is important to have
good audio - a link to this site can be found by clicking here.
After playing over a few more weeks, I decided to invest in an EQplus
by W2IHY. I was looking for something to give me just a tad more
presence to my transmitted signal and after listening to the audio
recordings on the W2IHY web site I took the opportunity to order one at
the same time as a friend of mine was doing the same. Before I ordered
I sent a few emails asking questions to Julius W2IHY - and he answered
all emails very quickly. The local UK distributor did a bit of a deal
for two units and a couple of days later it arrived.....
Above pictures with kind permission from Julius W2IHY
Connecting cables to the EQplus is straightforward, audio in and out
can be done via 5 pin DIN plugs - I ordered a few metalised connectors
from the local component store along with some screened mic cable. The
EQplus doesn't facilitate a 48V phantom supply, so I connected the Heil
PR-781 dynamic mic. The audio out goes straight into the Edirol FA-66
and the Behringer mixer is not used.
There are several settings to play with, including an equalizer,
compression & downward expander and an effects setting. I found I
needed to increase the mic gain on the Flexradio software in comparison
to the previous set-up. I tweaked the settings through a combination of
using a second radio and headphones as well as the HamAlyzer software.
Final tweaking was done through the help of very local stations to my
QTH. The picture below shows the dials all in opertaing their position.
I've got to say that I was a bit sceptical before I used this product.
But in actual fact it has enhanced my audio quality. Unsolicited good
audio reports are fairly common. Stations often comment that I sound
'louder' than what is reflected on their S meters. This to me is
'presence' on the transmit signal. I have a couple of transmit settings
- ranging from a DX mode, through to narrow voice, medium voice and
wideband Enhanced SSB. In the medium setting (100Hz to 3100Hz), audio
reports are generally very good for ragchew mode. I have slightly
adjusted the equalizer using monitor headphones with the EQplus. The
downward compander works better than the software noisegate - which
makes the audio choppy, with the
downward
compander I have been able to set it to get rid of background noise
without introducing any chop to my signal. I also have a miniscual
amount of reverb introduced to 'polish' the signal. When I get the
chance I shall 'graph' the audio output. The EQplus allows an audio
passband of about 5KHz, Julius has provided details to replace two
capacitors that will open up the passband to 10KHz. At this point in
time I do not intend to do this mod.
**24/04/2007** Recently I started to get feedback that it appeared that
there was RF getting into my audio. When I monitored transmit audio
through the monitor function on the SDR radio as well as a separate
receiver, indeed my audio appeared to crackle and distort when
transmitting. I spent some time tidying up cables, ensuring ferrites
were fitted, cables earthed etc etc. Yet the audio distortion was still
there. I then noticed that CPU usage was running at close to 100% upon
transmit - in the recent past I had installed a couple of new programs
on the PC that are resource hungry. By uninstalling these
programs, CPU usage dropped - and no more glitches in audio and
back to good reports. This is a useful footnote to be aware of.
Below are a couple of pics of the microphone and audio feed for the SDR radio.
I have managed to use the Behringer shock mount with the PR-781 microphone - bit of a tight fit but it works. The shock mount significantly reduces 'desk' noise!
The introduction of the Behringer Shark DSP110 was tried in conjunction with the condenser microphone which was too very sensitive, I am now using it with the Heil PR-781. The DSP110 provides a good boost to the dynamic mic and the noise gate is very effective - it has the best noise gate that I have tried to date.
The W2IHY 8 band audio equalizer does exactly what it is claimed to do. Audio is 'brightened' up.
Audio is fed thrugh to the W2IHY EQplus where I have a little tailoring using compression, downward expander and effects processor.
The three products together!