[hpsdr] PowerSDR/OpenHPSDR mRX PS v3.3.8 released

[Jim Sanford]

Doug and Warren:  Great stuff!!

Congratulations and thanks!

73,

Jim

wb4gcs at amsat.org



On 6/9/2016 6:51 PM, Doug W5WC wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> All,
>
> PowerSDR/OpenHPSDR mRX PS v3.3.8 has been released.
>
> This release can be downloaded from the openhpsdr.org website.
> http://openhpsdr.org/download.php
>
> This release contains the following changes:
>
> CRASH BUG FIX
>
> Some experienced a crash in 3.3.7, especially when changing DSP Buffer Sizes
> or during RX/TX transitions.  We believe this has been totally resolved.
>
> SIGNIFICANTLY LOWER LATENCY
>
> Receive latency is the time between when RF reaches your antenna and the
> corresponding audio is produced in your speaker or headphones.
> Similarly, transmit latency is, for example, the time between audio reaching
> your microphone and RF being on its way to your antenna.  For many SDRs,
> especially those with sharp "brick wall" filters, the latency can be much
> larger than you might expect.  Depending upon the radio design and various
> settings, SDR latencies can significantly exceed 100mS.  Long latencies can
> create problems for the operator in contest operation, high-speed break-in
> CW, and even SSB rapid-turnaround VOX operation.
>
> This release incorporates some technologies that allow us to achieve low
> latencies in the same category as leading conventional radios.
> Furthermore, we can do this with extremely sharp filters.
>
> First of all, a couple basics:
>
> * Sometime ago, we moved CW Transmit from software to the FPGA in the radio
> hardware.  This means that CW transmit latency was already very low, really
> based upon your delay settings which are chosen to avoid any hot-switching
> of relays.
>
> * It has always been the case that the Buffer Size setting on the
> Setup=>Audio/Primary tab effects latency.  The lower the size, the lower the
> latency.  However, the lower the size, the more CPU cycles are required.
> Depending upon the speed of your computer, you may be limited in how low you
> can go.  Fortunately, this is not likely to have such a large impact on your
> latency.  For a very rough estimate of the latency due to this buffer,
> divide the buffer size by the sample rate.  For example, a buffer of size
> 256, at a sample rate of 192K, contributes only about 256/192000 = 1.33mS.
>
> As of this release, there are some new features and corresponding controls
> to allow you to achieve much lower latency:
>
> * Up until this release, "Filter Size" and "DSP Buffer Size" have been the
> same and there has only been one setting, called "DSP Buffer Size."
> Filter Size determines how sharp your filters are; higher filter size leads
> to sharper filters.  However, higher DSP Buffer Size leads to more latency
> because we must collect enough samples to fill the buffer before the buffer
> can be processed.  As of this release, DSP Buffer Size and Filter Size are
> separate and can be set by mode on the Setup=>DSP/Options tab.  So, using a
> very low DSP Buffer size minimizes latency and using a high Filter Size
> leads to sharper filters.  The trade-off here is that using lower DSP buffer
> sizes requires somewhat more CPU cycles and using a high Filter Size does as
> well.  With a reasonably fast computer, you will likely be able to run at a
> DSP Buffer Size of 64, the minimum, except, perhaps, for the FM mode.  With
> filter sizes of 1024 or 2048, the sharpness of our filters rival the best
> radios. However, larger sizes, up to 16384, are available if you need them.
>
> * You now have a choice of Filter Type, with two types available:
> Linear Phase and Low Latency.  In the past, our filters have always been
> Linear Phase.  Linear Phase filters have the property that all frequencies
> are delayed by the same amount of time as the signal is processed through
> the filter.  This means that the time-domain waveform of a signal that is
> totally within the passband will look the same at the input of the filter
> and the output of the filter.  The Low Latency filter does not strictly
> comply with this same type of operation.  With the Low Latency filter,
> signals at frequencies very near the lower and upper edges of the passband
> may experience more delay than signals at other frequencies.  Comparing the
> two types of filters, beta testers have reported little, if any, difference
> in sound quality, no problems with several digital modes that have been
> tested, and no significant negative impacts at all from using the Low
> Latency filters.  However, both filter types are provided for your
> comparison and your choice.  Of course, the Low Latency filters provide
> lower latency.  In fact, the latency of Linear Phase filters increases
> linearly with Filter Size while the latency of the Low Latency filters is
> very low and nearly independent of Filter Size.
>
> Benchmark Comparisons:
>
> * For CW/SSB receive, using minimum Buffer Sizes and Low Latency filters,
> our beta testers have measured receive latencies in the 15mS to 20mS range.
> Using minimum Buffer Sizes and Linear Phase filters, the latencies are 25mS
> to 30mS for a Filter Size of 1024 and 35mS to 40mS for a Filter Size of
> 2048.  Using features such as noise blankers, EQ, and noise reduction will
> add some amount to that, depending upon the
> feature(s) and settings.  These numbers compare with ~65mS and ~120mS using
> DSP Buffer sizes of 1024 and 2048, respectively, in prior software releases.
>
> NOTE
> You WILL need to reset your database.
> This release will build a new wisdom file on first time use. Depending on
> your system, it may take a very long time to complete. Please be patient.
>
> MINOR CHANGES
> The following list of values and states where added to the TX Profiles
> - selection for mic in or line in
> - 20dB mic boost
> - line in gain
> - CESSB state
> - PureSignal state
>
> Thanks & 73,
>
> Warren, NR0V
> Doug, W5WC
>
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