refactor(dsp): add fc to pll()

src/dsp.jl

@@ -390,16 +390,19 @@ end
 
 """
 $(SIGNATURES)
-Phased-lock loop to track dominant carrier frequency in input signal.
+Phased-lock loop to track carrier frequency (approximately `fc`) in the input signal.
+If `fc` is not specified, the algorithm will attempt to track the dominant frequency.
 """
-function pll(x::AbstractVecOrMat, bandwidth=1e-3; fs=framerate(x))
+function pll(x::AbstractVecOrMat, fc=0.0, bandwidth=1e-3; fs=framerate(x))
+ fs = inHz(fs)
+ fc = inHz(fc)
  β = √bandwidth
  n = nchannels(x)
- ϕ = zeros(1,n)
- ω = zeros(1,n)
+ ϕ = zeros(1, n) # phase estimate
+ ω = zeros(1, n) # integrator
  y = similar(x, ComplexF64)
  for j ∈ 1:nframes(x)
- y[j,:] = cis.(ϕ)
+ y[j,:] = cis.(-2π * fc * (j-1)/fs .+ ϕ)
  Δϕ = angle.(x[j,:] .* conj.(y[j,:])) .* abs.(x[j,:])
  ω .+= bandwidth * Δϕ
  ϕ .+= β*Δϕ .+ ω

test/tests-core.jl

@@ -521,7 +521,7 @@ function test_dsp()
  x = cw(1kHz, 1s, 80kHz)
  x2 = x .+ 0.25*rand(rng, size(x)...) .+ 0.25im*rand(rng, size(x)...)
  e2 = √mean(abs2.(x[800:end] .- x2[800:end]))
- x3 = pll(x2)
+ x3 = pll(x2, 1kHz)
  @test meanfrequency(x3[800:end]) ≈ meanfrequency(x[800:end]) atol=0.1
  e3 = √mean(abs2.(x[800:end] .- x3[800:end]))
  @test e2/e3 > 3